all: omit unnecessary reassignment

The new version of Go has been optimized, and variables do not need
to be reassigned.

Change-Id: I0374b049271e53510f2b162f6821fb3595f2c8ff
Reviewed-on: https://go-review.googlesource.com/c/go/+/710835
Auto-Submit: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>

src/encoding/base32/base32_test.go

@@ -709,7 +709,6 @@ func TestBufferedDecodingPadding(t *testing.T) {
 	}
 
 	for _, testcase := range testcases {
-		testcase := testcase
 		pr, pw := io.Pipe()
 		go func() {
 			for _, chunk := range testcase.chunks {

src/encoding/xml/marshal_test.go

@@ -2561,7 +2561,6 @@ var closeTests = []struct {
 
 func TestClose(t *testing.T) {
 	for _, tt := range closeTests {
-		tt := tt
 		t.Run(tt.desc, func(t *testing.T) {
 			var out strings.Builder
 			enc := NewEncoder(&out)

src/io/fs/readdir_test.go

@@ -72,7 +72,6 @@ func TestFileInfoToDirEntry(t *testing.T) {
 	}
 
 	for _, test := range tests {
-		test := test
 		t.Run(test.path, func(t *testing.T) {
 			fi, err := Stat(testFs, test.path)
 			if err != nil {

src/testing/iotest/reader_test.go

@@ -238,7 +238,6 @@ func TestErrReader(t *testing.T) {
 	}
 
 	for _, tt := range cases {
-		tt := tt
 		t.Run(tt.name, func(t *testing.T) {
 			n, err := ErrReader(tt.err).Read(nil)
 			if err != tt.err {