Bump to go 1.21 in go.mod

tpl/internal/go_templates/htmltemplate/escape_test.go

@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build go1.13 && !windows
-// +build go1.13,!windows
+//go:build !windows
+// +build !windows
 
 package template
 
@@ -944,7 +944,6 @@ func TestEscapeSet(t *testing.T) {
 			t.Errorf("want\n\t%q\ngot\n\t%q", test.want, got)
 		}
 	}
-
 }
 
 func TestErrors(t *testing.T) {
@@ -1194,7 +1193,6 @@ func TestErrors(t *testing.T) {
 		// Check that we get the same error if we call Execute again.
 		if err := tmpl.Execute(buf, nil); err == nil || err.Error() != got {
 			t.Errorf("input=%q: unexpected error on second call %q", test.input, err)
-
 		}
 	}
 }