Update macos.cfg

We are seeing frequent timeouts of the macros Kokoro builds http://shortn/_dujMRLlVNN. Even successful ones take 38 mins, 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 {