Remove redundant $ symbol in google-cloudrun-docker.yml

[hellohawaii]

Fix a bug in google-cloudrun-docker.yml.

When defining the DOCKER_TAG variable, an extra dollar sign ($) was incorrectly prepended to the ${{ env.REGION }} expression. This caused the shell to misinterpret the variable during expansion.

Specifically, when env.REGION was set to us-central1-c, the shell attempted to expand $us-central1-c. Because the variable $us was undefined, it was replaced with an empty string, resulting in a malformed image tag that started with -central1-c.cThis tag format is invalid according to Docker's naming conventions, which caused the build step to fail.