%check: Run tests with %{_smp_mflags} instead of -j0

-j0 means: Run tests in parallel, automatic number of workers, according to CPU count
%{_smp_mflags} means: -j%{_smp_build_ncpus} where %{_smp_build_ncpus} is the CPU count by default

Hence, this makes no difference unless %{_smp_build_ncpus} is manually clamped.
In that case, we now respect the wishes of the builder/packager/etc.

python3.12.spec

@@ -1070,7 +1070,7 @@ CheckPython() {
   #  we don't ship it in the RPM package.
 
   LD_LIBRARY_PATH=$ConfDir $ConfDir/python -m test.regrtest \
-    -wW --slowest -j0 --timeout=1800 \
+    -wW --slowest %{_smp_mflags} --timeout=1800 \
     -i test_freeze_simple_script \
     %ifarch %{mips64}
     -x test_ctypes \