Resolve staticcheck linter reported issues

[blackpiglet]

Describe the problem/challenge you have
[A description of the current limitation/problem/challenge that you are experiencing.]
#5726 wants to enable more linters for Velero to comply with cluster-api's standard.
There is a significant gap between the cluster-api and Velero GolangCI enabled linters.
By far, staticcheck linter reports most issues, so try to resolve those first.

Describe the solution you'd like
[A clear and concise description of what you want to happen.]
This is the result of staticcheck linter scan result of Velero repository. There are 266 issues.
It looks like there is no whitelist setting available for staticcheck linter. dot_import_whitelist looks related, but it's used for dot-importing some external testing packages. It cannot make linter only to choose specific path of Velero code.

We need to resolve most of the reported issues to enable the staticcheck linter, because staticcheck makes the golangci check halt until timeout on my developing environment.

staticcheck_result_formatted.json

staticcheck_result_raw.json

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]

Environment:

• Velero version (use velero version):
• Kubernetes version (use kubectl version):
• Kubernetes installer & version:
• Cloud provider or hardware configuration:
• OS (e.g. from /etc/os-release):

Vote on this issue!

This is an invitation to the Velero community to vote on issues, you can see the project's top voted issues listed here.
Use the "reaction smiley face" up to the right of this comment to vote.

• 👍 for "The project would be better with this feature added"
• 👎 for "This feature will not enhance the project in a meaningful way"

[blackpiglet]

First install staticcheck linter binary, then run the linter to get the scan result.

# install staticcheck binary
go install honnef.co/go/tools/cmd/[email protected]

# run staticcheck linter
cd ~/go/src/github.com/vmware-tanzu/velero
staticcheck -f json ./... > staticcheck_result_raw.json

The result is ouputed as multiple JSONs. Need to integrate them into a JSON array to better display.

import json

results = []
for line in open('staticcheck_result_raw.json', 'r'):
    results.append(json.loads(line))

out_file = open("staticcheck_result_formatted.json", "w")
  
json.dump(results, out_file, indent = 2)
  
out_file.close()

Formatted JSON file is a bit long. Can split the file into several shards.

split -l 1000 staticcheck_result_formatted.json split_

[reasonerjt]

Let's target v1.11 to enable the check. However, there may be too many errors to fix, we'll skip the check for some of the packages and fix the issues iteratively in future patch releases.