refactor: simplify go-git cache

[ChristopherHX]

Doing a refs/*/ fetch seems unnecassary, short shas are rejected by the git protocol.

This fixes using HEAD as action version and let git decide to prefer tag over branch name using short form

Also reduces complexity.

Fixes #2206

Includes extended test cases and no longer fetches a repository from my account.

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ EDITORCONFIG	editorconfig-checker	2		0	0.01s
✅ REPOSITORY	gitleaks	yes		no	2.33s
✅ REPOSITORY	git_diff	yes		no	0.12s
✅ REPOSITORY	grype	yes		no	7.34s
✅ REPOSITORY	secretlint	yes		no	1.09s
✅ REPOSITORY	trivy-sbom	yes		no	0.61s
✅ REPOSITORY	trufflehog	yes		no	7.36s

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[mergify]

@ChristopherHX this pull request has failed checks 🛠

[codecov]

Codecov Report

Attention: 33 lines in your changes are missing coverage. Please review.

Comparison is base (5a80a04) 61.56% compared to head (2d3e685) 61.66%.
Report is 14 commits behind head on master.

Files	Patch %	Lines
pkg/runner/action_cache_offline_mode.go	0.00%	22 Missing ⚠️
pkg/container/docker_socket.go	85.52%	9 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2208      +/-   ##
==========================================
+ Coverage   61.56%   61.66%   +0.10%     
==========================================
  Files          53       55       +2     
  Lines        9002     9078      +76     
==========================================
+ Hits         5542     5598      +56     
- Misses       3020     3041      +21     
+ Partials      440      439       -1     

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