io-qcow2-iothreads-commit-active test fails in a "minimal" build of QEMU
Description of problem:
The build fails because of the `io-qcow2-iothreads-commit-active` test failure:

```
343/412 qemu:block / io-qcow2-iothreads-commit-active                 ERROR           1.66s   exit status 1
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stderr:
--- /tmp/guix-build-qemu-minimal-8.1.0.drv-0/qemu-8.1.0/tests/qemu-iotests/tests/iothreads-commit-active.out
+++ /tmp/guix-build-qemu-minimal-8.1.0.drv-0/qemu-8.1.0/b/qemu/scratch/qcow2-file-iothreads-commit-active/iothreads-commit-active.out.bad
@@ -11,13 +11,27 @@
 10 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)

 Launching VM...
-Creating some background I/O...
-{"return": {}}
-Starting active commit...
-{"return": {}}
-{"execute": "job-complete", "arguments": {"id": "job1"}}
-{"return": {}}
-{"data": {"device": "job1", "len": 131072, "offset": 131072, "speed": 0, "type": "commit"}, "event": "BLOCK_JOB_READY", "timestamp": {"microseconds": "USECS", "seconds": "SECS"}}
-{"data": {"device": "job1", "len": 131072, "offset": 131072, "speed": 0, "type": "commit"}, "event": "BLOCK_JOB_COMPLETED", "timestamp": {"microseconds": "USECS", "seconds": "SECS"}}
-{"execute": "job-dismiss", "arguments": {"id": "job1"}}
-{"return": {}}
+Traceback (most recent call last):
+  File "/tmp/guix-build-qemu-minimal-8.1.0.drv-0/qemu-8.1.0/python/qemu/machine/machine.py", line 436, in launch
+    self._launch()
+  File "/tmp/guix-build-qemu-minimal-8.1.0.drv-0/qemu-8.1.0/python/qemu/machine/machine.py", line 463, in _launch
+    self._pre_launch()
+  File "/tmp/guix-build-qemu-minimal-8.1.0.drv-0/qemu-8.1.0/tests/qemu-iotests/iotests.py", line 841, in _pre_launch
+    super()._pre_launch()
+  File "/tmp/guix-build-qemu-minimal-8.1.0.drv-0/qemu-8.1.0/python/qemu/machine/qtest.py", line 143, in _pre_launch
+    self._qtest = QEMUQtestProtocol(self._qtest_path, server=True)
+  File "/tmp/guix-build-qemu-minimal-8.1.0.drv-0/qemu-8.1.0/python/qemu/machine/qtest.py", line 54, in __init__
+    self._sock.bind(self._address)
+OSError: AF_UNIX path too long
+
+The above exception was the direct cause of the following exception:
+
+Traceback (most recent call last):
+  File "/tmp/guix-build-qemu-minimal-8.1.0.drv-0/qemu-8.1.0/tests/qemu-iotests/tests/iothreads-commit-active", line 65, in <module>
+    vm.launch()
+  File "/tmp/guix-build-qemu-minimal-8.1.0.drv-0/qemu-8.1.0/python/qemu/machine/machine.py", line 449, in launch
+    raise VMLaunchFailure(
+qemu.machine.machine.VMLaunchFailure: OSError: AF_UNIX path too long
+       Command: /tmp/guix-build-qemu-minimal-8.1.0.drv-0/qemu-8.1.0/b/qemu/tests/qemu-iotests/../../qemu-system-x86_64 -display none -vga none -chardev socket,id=mon,fd=3 -mon chardev=mon,mode=control -qtest unix:path=/tmp/guix-build-qemu-minimal-8.1.0.drv-0/tmptfjmlerc/qcow2-file-iothreads-commit-active/qemu-58979-qtest.sock -accel qtest -nodefaults -display none -accel qtest -object iothread,id=iothread0 -object throttle-group,x-bps-write=1048576,id=tg0 -blockdev file,node-name=disk0-file,filename=/tmp/guix-build-qemu-minimal-8.1.0.drv-0/qemu-8.1.0/b/qemu/scratch/qcow2-file-iothreads-commit-active/58979-disk0.img -blockdev qcow2,node-name=disk0-fmt,file=disk0-file -drive if=none,id=drive0,file=/tmp/guix-build-qemu-minimal-8.1.0.drv-0/qemu-8.1.0/b/qemu/scratch/qcow2-file-iothreads-commit-active/58979-disk0-snap.img,format=qcow2,cache=writeback,aio=threads,backing=disk0-fmt,node-name=disk0 -device virtio-scsi,iothread=iothread0 -device scsi-hd,drive=drive0 -blockdev file,filename=/tmp/guix-build-qemu-minimal-8.1.0.drv-0/qemu-8.1.0/b/qemu/scratch/qcow2-file-iothreads-commit-active/58979-mirror-src.img,node-name=mirror-src-file -blockdev qcow2,file=mirror-src-file,node-name=mirror-src -blockdev file,filename=/tmp/guix-build-qemu-minimal-8.1.0.drv-0/qemu-8.1.0/b/qemu/scratch/qcow2-file-iothreads-commit-active/58979-mirror-dst.img,node-name=mirror-dst-file -blockdev qcow2,file=mirror-dst-file,node-name=mirror-dst-fmt -blockdev throttle,throttle-group=tg0,file=mirror-dst-fmt,node-name=mirror-dst -device scsi-hd,drive=mirror-src
+       Output:
+

(test program exited with status code 1)
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```
Steps to reproduce:
1. Install GNU Guix on your GNU/Linux machine.
2. `guix time-machine --url=https://gitlab.com/Apteryks/guix --branch=qemu-minimal-io-qcow2-iothreads-commit-active-test-failure -- build qemu-minimal --keep-failed`
3. Observe the test failure.  The build artifacts are left under /tmp/guix-build-qemu-minimal-8.1.0.drv-0 to inspect.
Additional information:
Attached is the complete build log
[8xr1k7v10jp2wgbimib6f0s51ilqgj3z-qemu-minimal-8.1.0.drv.gz](/uploads/59a0f88a05715c18a6bdb44845b83a18/8xr1k7v10jp2wgbimib6f0s51ilqgj3z-qemu-minimal-8.1.0.drv.gz)