Set default rpm package summary value if it's missing

[m-czernek]

What does this PR change?

An RPM package may not set any summary in the RPM header. Technically, this is an invalid RPM package, but reposync can handle this case.

• DONE

Documentation

• No documentation needed: Internal bugfix

• DONE

Test coverage

ℹ️ If a major new functionality is added, it is strongly recommended that tests for the new functionality are added to the Cucumber test suite

• No tests: Internal bugfix

• DONE

Links

Issue(s): https://github.com/SUSE/spacewalk/issues/25668
Port(s): TODO

• DONE

Changelogs

Make sure the changelogs entries you are adding are compliant with https://github.com/uyuni-project/uyuni/wiki/Contributing#changelogs and https://github.com/uyuni-project/uyuni/wiki/Contributing#uyuni-projectuyuni-repository

If you don't need a changelog check, please mark this checkbox:

• No changelog needed

If you uncheck the checkbox after the PR is created, you will need to re-run changelog_test (see below)

Re-run a test

If you need to re-run a test, please mark the related checkbox, it will be unchecked automatically once it has re-run:

• Re-run test "changelog_test"
• Re-run test "backend_unittests_pgsql"
• Re-run test "java_pgsql_tests"
• Re-run test "schema_migration_test_pgsql"
• Re-run test "susemanager_unittests"
• Re-run test "javascript_lint"
• Re-run test "spacecmd_unittests"

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