Fix patch file path

Fixes errors when generating a to-be-applied patch like the following:
```sh
[13:26:24.999 Information] /tmp/tmprjqpg5.tmp: line 17: ../artifacts/proto.patch: No such file or directory
```

.yamato/protobuf-generation-test.yml

@@ -25,7 +25,7 @@ test_linux_protobuf_generation:
       git diff --exit-code -- :/ ":(exclude,top)$CS_PROTO_PATH/*.meta"                          \
       || { GIT_ERR=$?; echo "protobufs need to be regenerated, apply the patch uploaded to artifacts."; \
       echo "Apply the patch with the command 'git apply proto.patch'";                                  \
-      git diff -- :/ ":(exclude,top)$CS_PROTO_PATH/*.meta" > ../artifacts/proto.patch; exit $GIT_ERR; }
+      git diff -- :/ ":(exclude,top)$CS_PROTO_PATH/*.meta" > artifacts/proto.patch; exit $GIT_ERR; }
   triggers:
     cancel_old_ci: true
     expression: |