buildscripts: Increase macos.cfg timeout to 1h

We are seeing frequent Kokoro VM timeouts with the 45 minute setting.
Even successful builds take 38 mins which is close, so increasing the
timeout to 1 hour.

Author: kannanjgithub

buildscripts/kokoro/macos.cfg

@@ -2,7 +2,7 @@
 
 # Location of the continuous shell script in repository.
 build_file: "grpc-java/buildscripts/kokoro/macos.sh"
-timeout_mins: 45
+timeout_mins: 60
 
 # We always build mvn artifacts.
 action {