ci: install git in stock-Ubuntu baseline job (#4847)

The nodeJsBaselineAptCompatibility job runs `apt install --yes nodejs npm`
in an ubuntu:26.04 container. The test suite bootstraps throwaway repos via
`git init`, and the git binary only ever arrived as an apt Recommends of the
npm chain — never a hard dependency.

On 2026-06-25 that broke: with the identical image digest and identical
nodejs 22.22.1 / npm 9.2.0, apt stopped installing Recommends (logging
`Recommended packages: build-essential git ...` and skipping them), so git
was absent and ~189 git-dependent tests errored. Same commit had passed the
day before — purely an environment shift in the fast-moving 26.04 archive.

Install git explicitly so the job no longer relies on an un-guaranteed
Recommends default. This stays in the spirit of the job (stock apt packages,
no actions/setup-node); git is a standard system tool, not a Node shortcut.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: escapedcat

.github/workflows/CI.yml

@@ -113,8 +113,15 @@ jobs:
           apt update --yes
 
           # NOTE: do not change the below with an `actions/setup-node` step! or it
-          # would make this CI job entirely pointless
-          apt install --yes nodejs npm
+          # would make this CI job entirely pointless.
+          #
+          # `git` is needed because the test suite bootstraps throwaway repos via
+          # `git init`. It used to arrive as an apt Recommends of the npm chain,
+          # but on ubuntu:26.04 apt stopped pulling that recommend in (same image
+          # digest, same node/npm versions), so install it explicitly. The
+          # checkout step runs before this and uses the REST API fallback either
+          # way, which is fine — the tests create their own repos.
+          apt install --yes nodejs npm git
 
           # Ubuntu's bundled corepack (with stock Node) trips on the dynamic
           # ESM imports pnpm 11 uses at launch (ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING).