Remove unnecessary copies of loop variables (#28138)

server/channels/app/post_test.go

@@ -757,7 +757,6 @@ func TestMaxPostSize(t *testing.T) {
 	}
 
 	for _, testCase := range testCases {
-		testCase := testCase
 		t.Run(testCase.Description, func(t *testing.T) {
 			mockStore := &storetest.Store{}
 			defer mockStore.AssertExpectations(t)