feat(bare/worktree): only check remote branches if remote has 'fetch' config

[linrongbin16]

… configured

Regression Test

Platforms

• windows
• macOS
• linux

Tasks

• Use GitLink to copy git link.
• Use GitLink! to open git link in browser.
• Use GitLink blame to copy the /blame git link.
• Use GitLink! blame to open the /blame git link in browser.
• Copy git link in a symlink directory of git repo.
• Copy git link in an un-pushed git branch, and receive an expected error.
• Copy git link in a pushed git branch but edited file, and receive a warning says the git link could be wrong.

[linrongbin16]

relate: #107

[codecov]

Codecov Report

Attention: 9 lines in your changes are missing coverage. Please review.

Comparison is base (9d3f8de) 75.78% compared to head (666ef48) 76.43%.

Files	Patch %	Lines
lua/gitlinker/git.lua	66.66%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #143      +/-   ##
==========================================
+ Coverage   75.78%   76.43%   +0.65%     
==========================================
  Files          11       11              
  Lines         921      921              
==========================================
+ Hits          698      704       +6     
+ Misses        223      217       -6     

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