CI: Replace _ of in GHA workflow filenames with -

[akihironitta]

What does this PR do?

Fixes inconsistency in workflow filenames.

Docs changes will conflict with #13849, so I'll update them after the PR gets merged. WIP

TODO

• Update all occurences in the docs (readmes).
  • CircleCI badge: https://app.circleci.com/settings/project/github/Lightning-AI/lightning/status-badges
  • GHA badge: e.g. https://github.com/Lightning-AI/lightning/actions/workflows/ci-pytorch-test-full.yml

Does your PR introduce any breaking changes? If yes, please list them.

None

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cc @Borda @carmocca @akihironitta

[codecov]

Codecov Report

Merging #13917 (68f786c) into master (b25275c) will increase coverage by 15%.
The diff coverage is n/a.

❗ Current head 68f786c differs from pull request most recent head ea332fb. Consider uploading reports for the commit ea332fb to get more accurate results

@@            Coverage Diff            @@
##           master   #13917     +/-   ##
=========================================
+ Coverage      61%      76%    +15%     
=========================================
  Files         324      323      -1     
  Lines       26384    26526    +142     
=========================================
+ Hits        16169    20144   +3975     
+ Misses      10215     6382   -3833     

[Borda]

for me, the _ and - served as grouping so CI pytorch - test full become ci-pytorch_test-full

[akihironitta]

@Borda If you prefer _ to -, we can maybe keep it as is, but I'm favour of using - because it's still possible to group them with -, and I'm sure people in the team/community will start using them differently between the two, which leads to inconsistency as we currently have ci-* and ci_*, for example.

I created this PR because the inconsistency in naming was making it hard for me to prepare GHA badge links as well as document CI/CD.

[akihironitta]

@Borda I'm still in favour of this PR, but feel free to close this PR if you find this PR unreasonable.