Fix golangci-lint issues and warnings

[mathieu-benoit]

Signed-off-by: Mathieu Benoit [email protected]

Fixing: #22.

FYI, resources in this Org related to this (specifically around the value: 10 * time.Second):

• address Potential Slowloris Attack because ReadHeaderTimeout is not configured in the http.Server fulcio#735
• https://github.com/sigstore/cosign/blob/main/test/cmd/getoidctoken/main.go#L57

Also took the initiative to fix the following warnings by removing the deprecated linters now included in the unused linter:

level=warning msg="[runner] The linter 'structcheck' is deprecated (since v1.49.0) due to: The owner seems to have abandoned the linter.  Replaced by unused."
  level=warning msg="[runner] The linter 'golint' is deprecated (since v1.41.0) due to: The repository of the linter has been archived by the owner.  Replaced by revive."
  level=warning msg="[runner] The linter 'varcheck' is deprecated (since v1.49.0) due to: The owner seems to have abandoned the linter.  Replaced by unused."
  level=warning msg="[runner] The linter 'interfacer' is deprecated (since v1.38.0) due to: The repository of the linter has been archived by the owner. "
  level=warning msg="[runner] The linter 'deadcode' is deprecated (since v1.49.0) due to: The owner seems to have abandoned the linter.  Replaced by unused."

Finally, took also the initiative to fix the following warning by using golangci/golangci-lint-action v3:

Warning: The `save-state` command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

[cpanato]

thank you