FindGTest: Refactor test type checks to avoid cases triggering CMP0064

Update our if() conditions to avoid CMP0064 warnings when `${test_type}`
is equal to `TEST`.

Reported-by: David T. Chen <dchen@mail.nih.gov>

Modules/FindGTest.cmake

@@ -124,11 +124,11 @@ function(GTEST_ADD_TESTS executable extra_args)
           string(REGEX MATCH "${gtest_test_type_regex}" test_type ${hit})
 
           # Parameterized tests have a different signature for the filter
-          if(${test_type} STREQUAL "TEST_P")
+          if("x${test_type}" STREQUAL "xTEST_P")
             string(REGEX REPLACE ${gtest_case_name_regex}  "*/\\1.\\2/*" test_name ${hit})
-          elseif(${test_type} STREQUAL "TEST_F" OR ${test_type} STREQUAL "TEST")
+          elseif("x${test_type}" STREQUAL "xTEST_F" OR "x${test_type}" STREQUAL "xTEST")
             string(REGEX REPLACE ${gtest_case_name_regex} "\\1.\\2" test_name ${hit})
-          elseif(${test_type} STREQUAL "TYPED_TEST")
+          elseif("x${test_type}" STREQUAL "xTYPED_TEST")
             string(REGEX REPLACE ${gtest_case_name_regex} "\\1/*.\\2" test_name ${hit})
           else()
             message(WARNING "Could not parse GTest ${hit} for adding to CTest.")