refactor: Enable perfsprint; fix appeared lint issues

[alexandear]

The PR enables perfsprint linter and fixes the lint issues that appeared. This linter is mostly useful for suggesting errors.New instead of fmt.Errorf where formatting is not needed.

Details

❯ golangci-lint run
github/copilot.go:90:11: fmt.Errorf can be replaced with errors.New (perfsprint)
return fmt.Errorf("assignee type field is not set")
^
github/git_commits.go:132:20: fmt.Errorf can be replaced with errors.New (perfsprint)
return nil, nil, fmt.Errorf("commit must be provided")
^
github/orgs_properties.go:72:12: fmt.Errorf can be replaced with errors.New (perfsprint)
return fmt.Errorf("non-string value in string array")
^
github/pulls.go:355:20: fmt.Errorf can be replaced with errors.New (perfsprint)
return nil, nil, fmt.Errorf("pull must be provided")
^
github/git_commits_test.go:405:30: fmt.Errorf can be replaced with errors.New (perfsprint)
signer := mockSigner(t, "", fmt.Errorf("signer error"), "")
^

[gmlewis]

I'm fine with fmt.Errorf => errors.New but am not OK with fmt.Sprint => strconv.FormatInt.

[codecov]

Codecov Report

Attention: Patch coverage is 42.85714% with 4 lines in your changes missing coverage. Please review.

Project coverage is 93.29%. Comparing base (2b8c7fa) to head (3d9f8e2).
Report is 146 commits behind head on master.

Files with missing lines	Patch %	Lines
...xample/codespaces/newreposecretwithxcrypto/main.go	0.00%	1 Missing ⚠️
...xample/codespaces/newusersecretwithxcrypto/main.go	0.00%	1 Missing ⚠️
example/newreposecretwithxcrypto/main.go	0.00%	1 Missing ⚠️
github/pulls.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## master #3324 +/- ##
==========================================
- Coverage 97.72% 93.29% -4.43% 
==========================================
Files 153 171 +18 Lines 13390 11729 -1661 ==========================================
- Hits 13085 10943 -2142 - Misses 215 692 +477 - Partials 90 94 +4 

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[gmlewis]

Thank you, @alexandear !
LGTM.
Merging.