[DNM] go.mod: bump grpc to 1.39.0 to test data race fix

[adityamaru]

Testing grpc/grpc-go#4627.

Release note: None

[cockroach-teamcity]

This change is 

[adityamaru]

cc: @knz

• Bumped grpc to 1.39.0
• Added the patch in transport: fix race accessing s.recvCompress grpc/grpc-go#4627 to a vendor branch https://github.com/cockroachdb/vendored/commits/grpc-1.39.0-test.
• Ran make stressrace PKG=./pkg/gossip TESTS=TestClientNodeID TESTFLAGS='-v --show-logs' | tee out

Without the patch, we see a DATA RACE immediately.

With the patch I've gone ~7000 runs without failure:

[knz]

thank you!