[v15.0/forgejo]: chore: add modernizer linter (#11949)

**Backport: !11936**

- Go has a suite of small linters that helps with modernizing Go code by using newer functions and catching small mistakes, https://pkg.go.dev/golang.org/x/tools/go/analysis/passes/modernize.
- Enable this linter in golangci-lint.
- There's also [`go fix`](https://go.dev/blog/gofix), which is not yet released as a linter in golangci-lint: https://github.com/golangci/golangci-lint/pull/6385

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/11949
Reviewed-by: Mathieu Fenniak <mfenniak@noreply.codeberg.org>
Co-authored-by: Gusted <postmaster@gusted.xyz>
Co-committed-by: Gusted <postmaster@gusted.xyz>

services/gitdiff/csv.go

@@ -134,7 +134,7 @@ func createCsvDiffSingle(reader *csv.Reader, celltype TableDiffCellType) ([]*Tab
 			return nil, err
 		}
 		cells := make([]*TableDiffCell, len(row))
-		for j := 0; j < len(row); j++ {
+		for j := range row {
 			if celltype == TableDiffCellDel {
 				cells[j] = &TableDiffCell{LeftCell: row[j], Type: celltype}
 			} else {
@@ -365,11 +365,11 @@ func getColumnMapping(baseCSVReader, headCSVReader *csvReader) ([]int, []int) {
 	}
 
 	// Loops through the baseRow and see if there is a match in the head row
-	for i := 0; i < len(baseRow); i++ {
+	for i := range baseRow {
 		base2HeadColMap[i] = unmappedColumn
 		baseCell, err := getCell(baseRow, i)
 		if err == nil {
-			for j := 0; j < len(headRow); j++ {
+			for j := range headRow {
 				if head2BaseColMap[j] == -1 {
 					headCell, err := getCell(headRow, j)
 					if err == nil && baseCell == headCell {
@@ -390,7 +390,7 @@ func getColumnMapping(baseCSVReader, headCSVReader *csvReader) ([]int, []int) {
 
 // tryMapColumnsByContent tries to map missing columns by the content of the first lines.
 func tryMapColumnsByContent(baseCSVReader *csvReader, base2HeadColMap []int, headCSVReader *csvReader, head2BaseColMap []int) {
-	for i := 0; i < len(base2HeadColMap); i++ {
+	for i := range base2HeadColMap {
 		headStart := 0
 		for base2HeadColMap[i] == unmappedColumn && headStart < len(head2BaseColMap) {
 			if head2BaseColMap[headStart] == unmappedColumn {
@@ -424,7 +424,7 @@ func getCell(row []string, column int) (string, error) {
 // countUnmappedColumns returns the count of unmapped columns.
 func countUnmappedColumns(mapping []int) int {
 	count := 0
-	for i := 0; i < len(mapping); i++ {
+	for i := range mapping {
 		if mapping[i] == unmappedColumn {
 			count++
 		}

services/gitdiff/gitdiff.go

@@ -524,10 +524,7 @@ func ParsePatch(ctx context.Context, maxLines, maxLineCharacters, maxFiles int,
 
 	// OK let's set a reasonable buffer size.
 	// This should be at least the size of maxLineCharacters or 4096 whichever is larger.
-	readerSize := maxLineCharacters
-	if readerSize < 4096 {
-		readerSize = 4096
-	}
+	readerSize := max(maxLineCharacters, 4096)
 
 	input := bufio.NewReaderSize(reader, readerSize)
 	line, err := input.ReadString('\n')

services/gitdiff/gitdiff_test.go

@@ -445,7 +445,7 @@ index 0000000..6bb8f39
 `
 	diffBuilder.WriteString(diff)
 
-	for i := 0; i < 35; i++ {
+	for i := range 35 {
 		diffBuilder.WriteString("+line" + strconv.Itoa(i) + "\n")
 	}
 	diff = diffBuilder.String()
@@ -482,11 +482,11 @@ index 0000000..6bb8f39
 	diffBuilder.Reset()
 	diffBuilder.WriteString(diff)
 
-	for i := 0; i < 33; i++ {
+	for i := range 33 {
 		diffBuilder.WriteString("+line" + strconv.Itoa(i) + "\n")
 	}
 	diffBuilder.WriteString("+line33")
-	for i := 0; i < 512; i++ {
+	for range 512 {
 		diffBuilder.WriteString("0123456789ABCDEF")
 	}
 	diffBuilder.WriteByte('\n')

services/gitdiff/highlightdiff_test.go

@@ -101,7 +101,7 @@ func TestDiffWithHighlightPlaceholderExhausted(t *testing.T) {
 
 func TestDiffWithHighlightTagMatch(t *testing.T) {
 	totalOverflow := 0
-	for i := 0; i < 100; i++ {
+	for i := range 100 {
 		hcd := NewHighlightCodeDiff()
 		hcd.placeholderMaxCount = i
 		diffs := hcd.diffWithHighlight(