[chore] upgrade golangci-lint to v2.1.6 and migrate config (#4265)

Signed-off-by: nicole mikołajczyk <git@mkljczk.pl>

# Description

Contribution guidelines link to the golangci-lint documentation for the up-to-date version rather than [the legacy v1 doc](https://golangci.github.io/legacy-v1-doc/), which uses a different configuration schema. I migrated the config using the `golangci-lint migrate` command, moved the comments, adjusted staticcheck config and ensured the rules still work.

## Checklist

- [x] I/we have read the [GoToSocial contribution guidelines](https://codeberg.org/superseriousbusiness/gotosocial/src/branch/main/CONTRIBUTING.md).
- [ ] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
- [x] I/we have not leveraged AI to create the proposed changes.
- [ ] I/we have performed a self-review of added code.
- [x] I/we have written code that is legible and maintainable by others.
- [ ] I/we have commented the added code, particularly in hard-to-understand areas.
- [ ] I/we have made any necessary changes to documentation.
- [ ] I/we have added tests that cover new code.
- [ ] I/we have run tests and they pass locally with the changes.
- [ ] I/we have run `go fmt ./...` and `golangci-lint run`.

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4265
Co-authored-by: nicole mikołajczyk <git@mkljczk.pl>
Co-committed-by: nicole mikołajczyk <git@mkljczk.pl>

.woodpecker/pr.yaml

@@ -22,7 +22,7 @@ steps:
 
     # We use golangci-lint for linting.
     # See: https://golangci-lint.run/
-    image: golangci/golangci-lint:v1.64.8
+    image: golangci/golangci-lint:v2.1.6
     pull: true
 
     # https://woodpecker-ci.org/docs/administration/configuration/backends/docker#run-user