[release/7.0][workloads] Automatically calculate the net6 patch version

[steveisok]

Automatically calculate the net6 patch version based on the net7 patch version. This is to prevent any instance where we forget to bump it manually.

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[lewing]

main (net8) will need to know the matching downlevel net6 and net7 versions once we start inserting it as well.

cc @marcpopMSFT

[marcpopMSFT]

As mentioned offline, the installer repo main branch is maintained manually unfortunately, and we haven't found a solution for that. The risk of being off on the downlevel runtimes is less though for the main branch at least.

[carlossanlop]

@steveisok @lewing @mmitche should we get Tactics approval for this, or can we treat it as tell-mode?

BTW CI failure is known/unrelated/already fixed: #78778

[steveisok]

I think it's tell mode and should go in.

[carlossanlop]

CI failure is known/unrelated/already fixed: #78778
Signed off.
Merging now.