Enable more revive linter rules (#30608)

Noteable additions:

- `redefines-builtin-id` forbid variable names that shadow go builtins
- `empty-lines` remove unnecessary empty lines that `gofumpt` does not
remove for some reason
- `superfluous-else` eliminate more superfluous `else` branches

Rules are also sorted alphabetically and I cleaned up various parts of
`.golangci.yml`.

services/migrations/gitea_downloader.go

@@ -410,7 +410,6 @@ func (g *GiteaDownloader) GetIssues(page, perPage int) ([]*base.Issue, bool, err
 		return nil, false, fmt.Errorf("error while listing issues: %w", err)
 	}
 	for _, issue := range issues {
-
 		labels := make([]*base.Label, 0, len(issue.Labels))
 		for i := range issue.Labels {
 			labels = append(labels, g.convertGiteaLabel(issue.Labels[i]))

services/migrations/gitlab.go

@@ -421,7 +421,6 @@ func (g *GitlabDownloader) GetIssues(page, perPage int) ([]*base.Issue, bool, er
 		return nil, false, fmt.Errorf("error while listing issues: %w", err)
 	}
 	for _, issue := range issues {
-
 		labels := make([]*base.Label, 0, len(issue.Labels))
 		for _, l := range issue.Labels {
 			labels = append(labels, &base.Label{