fix(gas): Switch to dedicated Ruby release image, and update to the default Ruby and Toys installed in that image (#378)

Author: dazuma

.kokoro/gas/trigger-cloud.cfg

@@ -13,7 +13,7 @@ build_file: "ruby-common-tools/.kokoro/gas/trigger_trampoline.sh"
 # Configure the docker image for kokoro-trampoline.
 env_vars: {
   key: "TRAMPOLINE_IMAGE"
-  value: "us-central1-docker.pkg.dev/cloud-sdk-release-custom-pool/release-images/ruby-multi"
+  value: "us-central1-docker.pkg.dev/cloud-sdk-release-custom-pool/release-images/ruby-release"
 }
 
 # Entrypoint

.kokoro/gas/trigger-generic.cfg

@@ -13,7 +13,7 @@ build_file: "ruby-common-tools/.kokoro/gas/trigger_trampoline.sh"
 # Configure the docker image for kokoro-trampoline.
 env_vars: {
   key: "TRAMPOLINE_IMAGE"
-  value: "us-central1-docker.pkg.dev/cloud-sdk-release-custom-pool/release-images/ruby-multi"
+  value: "us-central1-docker.pkg.dev/cloud-sdk-release-custom-pool/release-images/ruby-release"
 }
 
 # Entrypoint

.kokoro/gas/trigger-protobuf.cfg

@@ -13,7 +13,7 @@ build_file: "ruby-common-tools/.kokoro/gas/trigger_trampoline.sh"
 # Configure the docker image for kokoro-trampoline.
 env_vars: {
   key: "TRAMPOLINE_IMAGE"
-  value: "us-central1-docker.pkg.dev/cloud-sdk-release-custom-pool/release-images/ruby-multi"
+  value: "us-central1-docker.pkg.dev/cloud-sdk-release-custom-pool/release-images/ruby-release"
 }
 
 # Entrypoint

.kokoro/gas/trigger.sh

@@ -8,6 +8,4 @@ export GEM_HOME=$HOME/.gem
 export PATH=$GEM_HOME/bin:$PATH
 
 cd gas
-rbenv local $RUBY_31_VERSION
-gem install --no-document toys:0.14.5
 toys gas kokoro-trigger -v