Switch to use the default instance.

tools/internal_ci/linux/grpc_bazel_on_foundry_base.sh

@@ -56,6 +56,7 @@ source tools/internal_ci/helper_scripts/prepare_build_linux_rc
   --extra_execution_platforms=//third_party/toolchains:rbe_ubuntu1604 \
   --host_platform=//third_party/toolchains:rbe_ubuntu1604 \
   --platforms=//third_party/toolchains:rbe_ubuntu1604 \
+  --remote_instance_name=grpc-testing/instances/default_instance \
   $1 \
   -- //test/... || FAILED="true"
 

tools/internal_ci/linux/grpc_msan_on_foundry.sh

@@ -65,6 +65,7 @@ source tools/internal_ci/helper_scripts/prepare_build_linux_rc
   --extra_execution_platforms=//third_party/toolchains:rbe_ubuntu1604 \
   --host_platform=//third_party/toolchains:rbe_ubuntu1604 \
   --platforms=//third_party/toolchains:rbe_ubuntu1604 \
+  --remote_instance_name=grpc-testing/instances/default_instance \
   -- //test/... || FAILED="true"
 
 # Sleep to let ResultStore finish writing results before querying

tools/internal_ci/linux/grpc_ubsan_on_foundry.sh

@@ -62,6 +62,7 @@ source tools/internal_ci/helper_scripts/prepare_build_linux_rc
   --host_platform=//third_party/toolchains:rbe_ubuntu1604 \
   --platforms=//third_party/toolchains:rbe_ubuntu1604 \
   --cache_test_results=no \
+  --remote_instance_name=grpc-testing/instances/default_instance \
   -- //test/... || FAILED="true"
 
 # Sleep to let ResultStore finish writing results before querying

tools/internal_ci/linux/pull_request/grpc_ubsan_on_foundry.sh

@@ -61,6 +61,7 @@ source tools/internal_ci/helper_scripts/prepare_build_linux_rc
   --extra_execution_platforms=//third_party/toolchains:rbe_ubuntu1604 \
   --host_platform=//third_party/toolchains:rbe_ubuntu1604 \
   --platforms=//third_party/toolchains:rbe_ubuntu1604 \
+  --remote_instance_name=grpc-testing/instances/default_instance \
   -- //test/... || FAILED="true"
 
 if [ "$FAILED" != "" ]