Reenable test_gdb on most archs except arm and s390x

gdb has been fixed in Rawhide:
https://bugzilla.redhat.com/show_bug.cgi?id=1638798
https://bugzilla.redhat.com/show_bug.cgi?id=1634781

Install also gdb in selftest to no longer skip test_gdb
on the x86_64 CI.

But test_gdb is still skipped on armv7hl:
https://bugzilla.redhat.com/show_bug.cgi?id=1196181

And skipped on s390x:
https://bugzilla.redhat.com/show_bug.cgi?id=1678277

python38.spec

@@ -978,6 +978,10 @@ CheckPython() {
   # our non-standard decorators take effect on the relevant tests:
   #   @unittest._skipInRpmBuild(reason)
   #   @unittest._expectedFailureInRpmBuild
+  # test_gdb skipped on armv7hl:
+  #   https://bugzilla.redhat.com/show_bug.cgi?id=1196181
+  # test_gdb skipped on s390x:
+  #   https://bugzilla.redhat.com/show_bug.cgi?id=1678277
   # test_asyncio skipped:
   #   https://bugs.python.org/issue35998
   WITHIN_PYTHON_RPM_BUILD= \
@@ -985,7 +989,9 @@ CheckPython() {
     -wW --slowest -j0 \
     -x test_distutils \
     -x test_bdist_rpm \
+    %ifarch %{arm} s390x
     -x test_gdb \
+    %endif
     %ifarch %{mips64}
     -x test_ctypes \
     %endif

tests/tests.yml

@@ -16,6 +16,7 @@
         run: VERSION=3.8 X="-x test_socket -x test_asyncgen -x test_asyncio -x test_compile -x test_concurrent_futures -x test_itertools -x test_multiprocessing_fork -x test_multiprocessing_forkserver -x test_shutil -x test_time -x test_multiprocessing_spawn -x test_threading -x test_wsgiref" ./parallel.sh
     required_packages:
     - gcc  # for extension building in venv and selftest
+    - gdb  # for test_gdb
     - python38  # the test subject
     - python3-tox  # for venv tests
     - glibc-all-langpacks # for locale tests