Update gtest.cc

fix a broken link

googletest/src/gtest.cc

@@ -6037,7 +6037,7 @@ bool ShouldRunTestOnShard(int total_shards, int shard_index, int test_id) {
 // each TestSuite and TestInfo object.
 // If shard_tests == true, further filters tests based on sharding
 // variables in the environment - see
-// https://github.com/google/googletest/blob/master/googletest/docs/advanced.md
+// https://github.com/google/googletest/blob/main/docs/advanced.md
 // . Returns the number of tests that should run.
 int UnitTestImpl::FilterTests(ReactionToSharding shard_tests) {
   const int32_t total_shards = shard_tests == HONOR_SHARDING_PROTOCOL