Update googletest github links

Replace instances of "master" in github links

Change-Id: Iee373a91056d72803cfdd1684a362d9434a71ff7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3353108
Reviewed-by: Erik Staab <[email protected]>
Reviewed-by: Eric Willigers <[email protected]>
Reviewed-by: Nico Weber <[email protected]>
Commit-Queue: Nico Weber <[email protected]>
Owners-Override: Nico Weber <[email protected]>
Cr-Commit-Position: refs/heads/main@{#959901}
diff --git a/docs/testing/testing_in_chromium.md b/docs/testing/testing_in_chromium.md
index d3b918d..15be289 100644
--- a/docs/testing/testing_in_chromium.md
+++ b/docs/testing/testing_in_chromium.md
@@ -179,7 +179,7 @@
 test]" has instructions on how to disable a flaky test.
 
 [gtest]: https://github.com/google/googletest
-[Simple gtests]: https://github.com/google/googletest/blob/master/docs/primer.md#simple-tests
+[Simple gtests]: https://github.com/google/googletest/blob/main/docs/primer.md#simple-tests
 [Junit]: https://developer.android.com/training/testing/junit-rules
 [Instrumentation Tests]: https://chromium.googlesource.com/chromium/src/+/main/testing/android/docs/instrumentation.md
 [EarlGrey]: https://github.com/google/EarlGrey