Update base image of Cloud Build deploy image (#215)

Author: parlough

cloud_build/firebase-ghcli/Dockerfile

@@ -1,14 +1,14 @@
-FROM gcr.io/gcp-runtimes/ubuntu_20_0_4
+FROM marketplace.gcr.io/google/debian12
 
-# Install github cli
+# Install the GitHub cli.
 RUN apt update && apt install -y \
     curl \
     gpg
 RUN curl -fsSL https://cli.github.com/packages/githubcli-archive-keyring.gpg | gpg --dearmor -o /usr/share/keyrings/githubcli-archive-keyring.gpg;
 RUN echo "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/githubcli-archive-keyring.gpg] https://cli.github.com/packages stable main" | tee /etc/apt/sources.list.d/github-cli.list > /dev/null;
 RUN apt update && apt install -y gh;
 
-# Install node and npm
+# Install the latest LTS of Node, which also includes npm.
 RUN mkdir -p /etc/apt/keyrings
 RUN curl -fsSL https://deb.nodesource.com/gpgkey/nodesource-repo.gpg.key | gpg --dearmor -o /etc/apt/keyrings/nodesource.gpg
 ENV NODE_MAJOR=20

cloud_build/firebase-ghcli/README.md

@@ -1,18 +1,20 @@
 ## Summary
-This directory contains a Dockerfile that provides access to firebase tools and
-the Github CLI. This image is used to deploy various Dart/Flutter websites to
-firebase in both production and staging, and is also used to comment on Github
-PRs.
 
+This directory contains a Dockerfile that provides access to
+Node/NPM, Firebase CLI tools, and the GitHub CLI.
+This image is used to deploy various Dart/Flutter websites to
+Firebase in both production and staging, and is
+also used to comment staging links on GitHub PRs.
 
 ## Installed tools
-* Github CLI
+
+* GitHub CLI
 * Node/NPM
 * Firebase Tools
 
-
 ## Additional information
-When the dockerfile or cloud build template in this directory is changed in a
-PR, the cloud build template is triggered and a new version of the image is
-deployed as the latest version in Container Registry under the `flutter-dev`
-project in GCP.
+
+When the `Dockerfile` file or `cloudbuild.yaml` template in this directory
+are changed in a PR, the cloud build template is triggered and
+a new version of the image is deployed as the latest version in
+Container Registry under the `flutter-dev` project in GCP.