Run gopls modernize on codebase (#34751)

Recent modernize fixes:
https://github.com/golang/tools/commits/master/gopls/internal/analysis/modernize

services/pull/merge.go

@@ -8,6 +8,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"maps"
 	"os"
 	"path/filepath"
 	"regexp"
@@ -95,9 +96,7 @@ func getMergeMessage(ctx context.Context, baseGitRepo *git.Repository, pr *issue
 				vars["HeadRepoOwnerName"] = pr.HeadRepo.OwnerName
 				vars["HeadRepoName"] = pr.HeadRepo.Name
 			}
-			for extraKey, extraValue := range extraVars {
-				vars[extraKey] = extraValue
-			}
+			maps.Copy(vars, extraVars)
 			refs, err := pr.ResolveCrossReferences(ctx)
 			if err == nil {
 				closeIssueIndexes := make([]string, 0, len(refs))