style: gofumpt all the things (#9829)

Literally `gofumpt -w .` from the top level dir. Guaranteed to be minor
style changes only and nothing else.

@imsodin per request?

lib/fs/casefs_test.go

@@ -40,7 +40,7 @@ func testRealCase(t *testing.T, fsys Filesystem) {
 	testFs := newCaseFilesystem(fsys)
 	comps := []string{"Foo", "bar", "BAZ", "bAs"}
 	path := filepath.Join(comps...)
-	testFs.MkdirAll(filepath.Join(comps[:len(comps)-1]...), 0777)
+	testFs.MkdirAll(filepath.Join(comps[:len(comps)-1]...), 0o777)
 	fd, err := testFs.Create(path)
 	if err != nil {
 		t.Fatal(err)
@@ -93,7 +93,7 @@ func testRealCaseSensitive(t *testing.T, fsys Filesystem) {
 	names[0] = "foo"
 	names[1] = strings.ToUpper(names[0])
 	for _, n := range names {
-		if err := testFs.MkdirAll(n, 0777); err != nil {
+		if err := testFs.MkdirAll(n, 0o777); err != nil {
 			if IsErrCaseConflict(err) {
 				t.Skip("Filesystem is case-insensitive")
 			}