[libtooling][clang-tidy] Fix compiler warnings in testcase [NFC]

[libtooling][clang-tidy] Fix compiler warnings in testcase [NFC]

Without the fix we get:

06:31:09 In file included from ../../clang-tools-extra/unittests/clang-tidy/ClangTidyDiagnosticConsumerTest.cpp:3:
06:31:09 ../utils/unittest/googletest/include/gtest/gtest.h:1392:11: error: comparison of integers of different signs: 'const int' and 'const unsigned int' [-Werror,-Wsign-compare]
06:31:09   if (lhs == rhs) {
06:31:09       ~~~ ^  ~~~
06:31:09 ../utils/unittest/googletest/include/gtest/gtest.h:1421:12: note: in instantiation of function template specialization 'testing::internal::CmpHelperEQ<int, unsigned int>' requested here
06:31:09     return CmpHelperEQ(lhs_expression, rhs_expression, lhs, rhs);
06:31:09            ^
06:31:09 ../../clang-tools-extra/unittests/clang-tidy/ClangTidyDiagnosticConsumerTest.cpp:60:3: note: in instantiation of function template specialization 'testing::internal::EqHelper<false>::Compare<int, unsigned int>' requested here
06:31:09   EXPECT_EQ(4, Errors[0].Message.FileOffset);
06:31:09   ^
06:31:09 ../utils/unittest/googletest/include/gtest/gtest.h:1924:63: note: expanded from macro 'EXPECT_EQ'
06:31:09                       EqHelper<GTEST_IS_NULL_LITERAL_(val1)>::Compare, \
06:31:09                                                               ^
06:31:09 ../utils/unittest/googletest/include/gtest/gtest.h:1392:11: error: comparison of integers of different signs: 'const int' and 'const unsigned long' [-Werror,-Wsign-compare]
06:31:09   if (lhs == rhs) {
06:31:09       ~~~ ^  ~~~
06:31:09 ../utils/unittest/googletest/include/gtest/gtest.h:1421:12: note: in instantiation of function template specialization 'testing::internal::CmpHelperEQ<int, unsigned long>' requested here
06:31:09     return CmpHelperEQ(lhs_expression, rhs_expression, lhs, rhs);
06:31:09            ^
06:31:09 ../../clang-tools-extra/unittests/clang-tidy/ClangTidyDiagnosticConsumerTest.cpp:64:3: note: in instantiation of function template specialization 'testing::internal::EqHelper<false>::Compare<int, unsigned long>' requested here
06:31:09   EXPECT_EQ(1, Errors[0].Message.Ranges.size());
06:31:09   ^
06:31:09 ../utils/unittest/googletest/include/gtest/gtest.h:1924:63: note: expanded from macro 'EXPECT_EQ'
06:31:09                       EqHelper<GTEST_IS_NULL_LITERAL_(val1)>::Compare, \
06:31:09                                                               ^
06:31:09 2 errors generated.