MM-57245: Bump up Go version to 1.21 (#26512)

* MM-57245: Bump up Go version to 1.21

https://mattermost.atlassian.net/browse/MM-57245
```release-note
NONE
```

server/cmd/mmctl/commands/system_test.go

@@ -28,7 +28,7 @@ func (s *MmctlUnitTestSuite) TestGetBusyCmd() {
 
 		s.client.
 			EXPECT().
-			GetServerBusy(context.Background()).
+			GetServerBusy(context.TODO()).
 			Return(sbs, &model.Response{}, nil).
 			Times(1)
 
@@ -47,7 +47,7 @@ func (s *MmctlUnitTestSuite) TestGetBusyCmd() {
 
 		s.client.
 			EXPECT().
-			GetServerBusy(context.Background()).
+			GetServerBusy(context.TODO()).
 			Return(sbs, &model.Response{}, nil).
 			Times(1)
 
@@ -62,7 +62,7 @@ func (s *MmctlUnitTestSuite) TestGetBusyCmd() {
 		printer.Clean()
 		s.client.
 			EXPECT().
-			GetServerBusy(context.Background()).
+			GetServerBusy(context.TODO()).
 			Return(nil, &model.Response{}, errors.New("mock error")).
 			Times(1)
 
@@ -83,7 +83,7 @@ func (s *MmctlUnitTestSuite) TestSetBusyCmd() {
 
 		s.client.
 			EXPECT().
-			SetServerBusy(context.Background(), minutes*60).
+			SetServerBusy(context.TODO(), minutes*60).
 			Return(&model.Response{StatusCode: http.StatusOK}, nil).
 			Times(1)
 
@@ -121,7 +121,7 @@ func (s *MmctlUnitTestSuite) TestClearBusyCmd() {
 		printer.Clean()
 		s.client.
 			EXPECT().
-			ClearServerBusy(context.Background()).
+			ClearServerBusy(context.TODO()).
 			Return(&model.Response{StatusCode: http.StatusOK}, nil).
 			Times(1)
 
@@ -136,7 +136,7 @@ func (s *MmctlUnitTestSuite) TestClearBusyCmd() {
 		printer.Clean()
 		s.client.
 			EXPECT().
-			ClearServerBusy(context.Background()).
+			ClearServerBusy(context.TODO()).
 			Return(&model.Response{StatusCode: http.StatusBadRequest}, errors.New("mock error")).
 			Times(1)
 
@@ -154,7 +154,7 @@ func (s *MmctlUnitTestSuite) TestServerVersionCmd() {
 		expectedVersion := "1.23.4.dev"
 		s.client.
 			EXPECT().
-			GetPing(context.Background()).
+			GetPing(context.TODO()).
 			Return("", &model.Response{ServerVersion: expectedVersion}, nil).
 			Times(1)
 
@@ -170,7 +170,7 @@ func (s *MmctlUnitTestSuite) TestServerVersionCmd() {
 
 		s.client.
 			EXPECT().
-			GetPing(context.Background()).
+			GetPing(context.TODO()).
 			Return("", &model.Response{}, errors.New("mock error")).
 			Times(1)
 
@@ -188,7 +188,7 @@ func (s *MmctlUnitTestSuite) TestServerStatusCmd() {
 		expectedStatus := map[string]string{"status": "OK"}
 		s.client.
 			EXPECT().
-			GetPingWithOptions(context.Background(), model.SystemPingOptions{
+			GetPingWithOptions(context.TODO(), model.SystemPingOptions{
 				FullStatus:    true,
 				RESTSemantics: true,
 			}).
@@ -207,7 +207,7 @@ func (s *MmctlUnitTestSuite) TestServerStatusCmd() {
 
 		s.client.
 			EXPECT().
-			GetPingWithOptions(context.Background(), model.SystemPingOptions{
+			GetPingWithOptions(context.TODO(), model.SystemPingOptions{
 				FullStatus:    true,
 				RESTSemantics: true,
 			}).