tests/unit/test-blockjob: Disable complete_in_standby test

The blockjob/complete_in_standby test is flaky and fails
intermittently in CI:

172/621 qemu:unit / test-blockjob
           ERROR           0.26s   killed by signal 6 SIGABRT
11:03:46 MALLOC_PERTURB_=176
G_TEST_SRCDIR=/Users/pm215/src/qemu-for-merges/tests/unit
G_TEST_BUILDDIR=/Users/pm215/src/qemu-for-merges/build/all/tests/unit
/Users/pm215/src/qemu-for-merges/build/all/tests/unit/test-blockjob
--tap -k
----------------------------------- output -----------------------------------
stdout:
# random seed: R02S8c79d6e1c01ce0b25475b2210a253242
1..9
# Start of blockjob tests
ok 1 /blockjob/ids
stderr:
Assertion failed: (job->status == JOB_STATUS_STANDBY), function
test_complete_in_standby, file ../../tests/unit/test-blockjob.c, line
499.

Seen on macOS/x86_64, FreeBSD 13/x86_64, msys2-64bit, eg:

https://gitlab.com/qemu-project/qemu/-/jobs/3872508803
https://gitlab.com/qemu-project/qemu/-/jobs/3950667240

Disable this subtest until somebody has time to investigate.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20230317143534.1481947-1-peter.maydell@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>
(cherry picked from commit b6903cb)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

tests/unit/test-blockjob.c

@@ -531,6 +531,13 @@ int main(int argc, char **argv)
     g_test_add_func("/blockjob/cancel/standby", test_cancel_standby);
     g_test_add_func("/blockjob/cancel/pending", test_cancel_pending);
     g_test_add_func("/blockjob/cancel/concluded", test_cancel_concluded);
-    g_test_add_func("/blockjob/complete_in_standby", test_complete_in_standby);
+
+    /*
+     * This test is flaky and sometimes fails in CI and otherwise:
+     * don't run unless user opts in via environment variable.
+     */
+    if (getenv("QEMU_TEST_FLAKY_TESTS")) {
+        g_test_add_func("/blockjob/complete_in_standby", test_complete_in_standby);
+    }
     return g_test_run();
 }