Align the Ruby, Node.js, and npm install path with the rest of the
config. Three separate upstream installers were being invoked via
\`curl ... | bash\` or unlocked \`npm install\`:
- RVM's \`get.rvm.io/stable\` installer (mutable upstream script).
Replace with a shallow git clone of the rvm/rvm repo at tag 1.29.12
and verify HEAD matches the published commit SHA before running the
local \`./install\` script. Same pattern already used for the
helm-unittest plugin in .github/workflows/helm_unit_test.yml.
- NodeSource's \`deb.nodesource.com/setup_18.x\` piped into sudo bash.
Replace with a direct download of the Node.js 18.20.8 linux-x64
tarball from nodejs.org, verified against the published
SHASUMS256.txt digest before extraction.
- \`npm install @google-cloud/vertexai @google/generative-ai\` and
\`--save-dev jest\` resolved fresh from the npm registry on every
run. Add \`tests/pass_through_tests/package.json\` with pinned
direct-dep versions and commit the generated package-lock.json, then
switch CI to \`npm ci\` (exact lockfile install, fails on drift).
Also scopes the Ruby+JS test runners to \`tests/pass_through_tests/\`
so they pick up the committed package.json rather than writing
node_modules at repo root.
