Ignore sockets when loading keys

[Matir]

If a user uses ControlMaster in OpenSSH, UNIX sockets often appear in their ~/.ssh directory. These fail loading as a key. This skips those sockets in the filesystem.

Fixes #101.

[codecov-commenter]

Codecov Report

Merging #102 (0aea289) into main (bfaa7d1) will decrease coverage by 0.42%.
The diff coverage is 42.85%.

@@            Coverage Diff             @@
##             main     #102      +/-   ##
==========================================
- Coverage   80.92%   80.49%   -0.43%     
==========================================
  Files          16       16              
  Lines        1227     1241      +14     
==========================================
+ Hits          993      999       +6     
- Misses        173      179       +6     
- Partials       61       63       +2     

Impacted Files	Coverage Δ
internal/storage/fs/key.go	67.46% <42.85%> (-3.08%)	⬇️

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[slok]

Hey @Matir! Thanks for the contribution! I didn't have this case myself, so I appreciate a lot the use case you found.

I fixed the linting and add some tests. Should be ready to be merged

[slok]

@Matir there is a new release with this fix. v0.6.1

Thanks again!