fix: use %{python3} in mock-core-configs %check, add release note

On EPEL-8 the `python3` command is not on PATH (only
/usr/libexec/platform-python), so the %check step failed with
"python3: command not found" and broke the Copr build.  The spec
already defines `%global python3 /usr/libexec/platform-python` for
el8 (and the standard macro on Fedora/RHEL10+), so use `%{python3}`
instead of the bare `python3`.

Add a release-notes fragment for the new test.

Assisted-By: pi

Author: pkking

mock-core-configs/mock-core-configs.spec

@@ -86,7 +86,7 @@ sed -i "s~@MOCK_DOCS@~$mock_docs~" %{buildroot}%{_sysconfdir}/mock/site-defaults
 %check
 # Validate the shipped templates directly from the source tree (the configs
 # live in mock-core-configs, not the mock package).
-PYTHONPATH=. python3 -m pytest tests
+PYTHONPATH=. %{python3} -m pytest tests
 
 %post
 if [ -s /etc/os-release ]; then

releng/release-notes-next/openeuler-configs-metalink-test.feature.md

@@ -0,0 +1,4 @@
+Add a `%check` test to mock-core-configs that asserts openEuler source
+repositories use the literal `openEuler-<version>` directory in
+`metalink ... path=` URLs rather than the untranslated `$releasever`,
+which the metalink `path=` form does not expand.