fix: fix fallback to Git tag if VCS is unavailable

[maxbrunet]

When version is unavailable from the VCS, build info always returns (devel) as version

Tested without .git directory:

$ make kubelogin GIT_TAG=v0.1.4
rm -f bin/darwin_arm64/kubelogin
CGO_ENABLED=0 go build -o bin/darwin_arm64/kubelogin -ldflags "-X main.gitTag=v0.1.4"

$ "bin/$(go env GOOS)_$(go env GOARCH)/kubelogin" --version
kubelogin version
git hash: v0.1.4
Go version: go1.23.1
Build time: unknown
Platform: darwin/arm64

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 65.70%. Comparing base (cabc5a9) to head (00148d4).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
version.go	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #530      +/-   ##
==========================================
- Coverage   65.90%   65.70%   -0.20%     
==========================================
  Files          29       29              
  Lines        2050     2050              
==========================================
- Hits         1351     1347       -4     
- Misses        626      629       +3     
- Partials       73       74       +1     

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[weinong]

documenting what it looks like when vcs is not present

./bin/linux_amd64/kubelogin --version
kubelogin version
git hash: (devel)
Go version: go1.21.11
Build time: unknown
Platform: linux/amd64

[weinong]

LGTM