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`.

(cherry picked from commit 74f0c84fa4245a20ce6fb87dac1faf2aeeded2a2)

Conflicts:
	.golangci.yml
	apply the linter recommendations to Forgejo code as well

modules/templates/mailer.go

@@ -84,9 +84,8 @@ func Mailer(ctx context.Context) (*texttmpl.Template, *template.Template) {
 			if err = buildSubjectBodyTemplate(subjectTemplates, bodyTemplates, tmplName, content); err != nil {
 				if firstRun {
 					log.Fatal("Failed to parse mail template, err: %v", err)
-				} else {
-					log.Error("Failed to parse mail template, err: %v", err)
 				}
+				log.Error("Failed to parse mail template, err: %v", err)
 			}
 		}
 	}