go/types, types2: always accept type parameters when running Manual test

This makes it easier to run tests on existing generic code that is
not using the `.go2` ending currently used by type checker tests.

For #49074.

Change-Id: I1501463c55dbe1d709918786e1a43b6d1bf1629a
Reviewed-on: https://go-review.googlesource.com/c/go/+/357050
Trust: Robert Griesemer <[email protected]>
Run-TryBot: Robert Griesemer <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
TryBot-Result: Go Bot <[email protected]>

Author: griesemer

src/cmd/compile/internal/types2/check_test.go

@@ -99,7 +99,7 @@ func testFiles(t *testing.T, filenames []string, colDelta uint, manual bool) {
 	}
 
 	var mode syntax.Mode
-	if strings.HasSuffix(filenames[0], ".go2") {
+	if strings.HasSuffix(filenames[0], ".go2") || manual {
 		mode |= syntax.AllowGenerics
 	}
 	// parse files and collect parser errors

src/go/types/check_test.go

@@ -210,7 +210,7 @@ func testFiles(t *testing.T, sizes Sizes, filenames []string, srcs [][]byte, man
 	}
 
 	mode := parser.AllErrors
-	if !strings.HasSuffix(filenames[0], ".go2") {
+	if !strings.HasSuffix(filenames[0], ".go2") && !manual {
 		mode |= typeparams.DisallowParsing
 	}