Fix Rocky minor version strict typing

[Alex-Welsh]

I ran the pulp-repo-sync.yml and got a very long error trace that ended like this:

No variable found with this name: stackhpc_pulp_repo_doca_2_9_1_rhel9_7_version 

After a bit of fishing, I found that the issue was I had set:
stackhpc_pulp_repo_rocky_9_minor_version: 7
and not
stackhpc_pulp_repo_rocky_9_minor_version: '7'
i.e. the minor version was an integer, not a string.
That meant this this lookup failed:

stackhpc_pulp_doca_version_matrix:
    "6": 2.9.3
    "7": 3.2.1

Fixed by a string filter on the lookup. Same fix applied to other instances where the minor version is used

[elelaysh]

LGTM, thanks for the fix

[gemini-code-assist]

Code Review

This pull request addresses a bug where an integer-typed Rocky minor version caused a lookup failure in dictionaries with string keys. The changes correctly apply the | string filter to the version variable before using it as a dictionary key. My review includes a suggestion to improve the robustness of one of the lookups by using the .get() method to provide a default value, which corrects a subtle issue with the current use of the default filter.