tpl: Sync go_templates for Go 1.18

Using Go tag go1.18 4aa1efed4853ea067d665a952eee77c52faac774

Updates #9677

tpl/internal/go_templates/texttemplate/multi_test.go

@@ -2,6 +2,7 @@
 // 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
 
 package template
@@ -454,3 +455,13 @@ func TestIssue19294(t *testing.T) {
 		}
 	}
 }
+
+// Issue 48436
+func TestAddToZeroTemplate(t *testing.T) {
+	tree, err := parse.Parse("c", cloneText3, "", "", nil, builtins())
+	if err != nil {
+		t.Fatal(err)
+	}
+	var tmpl Template
+	tmpl.AddParseTree("x", tree["c"])
+}