[ci] Cache Chrome binary across CI runs for Browser Run tests

Browser Run tests in `packages/miniflare/test/plugins/browser/index.spec.ts`
and the `fixtures/browser-run` fixture call into `@puppeteer/browsers`
to ensure Chrome is downloaded into the global Wrangler cache. Every
CI run currently re-downloads ~150 MB of Chrome from scratch because
the cache directory is per-runner-instance and not shared between runs.

Add an `actions/cache@v4` step keyed on the OS + the Chrome version
hardcoded in `packages/miniflare/src/index.ts` (`126.0.6478.182")`,
restoring/saving `~/.cache/.wrangler/chrome` (Linux),
`~/Library/Caches/.wrangler/chrome` (macOS), and
`~/AppData/Local/xdg.cache/.wrangler/chrome` (Windows).

Benefits:
- Cuts ~150 MB and the associated download time off cold CI runs.
- Reduces the surface area for the intermittent partial-extraction
  race that surfaces as `The browser folder (...) exists but the
  executable (...) is missing` (see #13971 for the diagnostic that
  exposed this, #13980 for the in-process recovery layer). When the
  cache is warm and the binary is already extracted, this race can't
  fire at all because `install()` short-circuits.

The cache step runs for the `packages-and-tools` suite on all three
OSes and for the `fixtures` suite on macOS + Windows (the Browser Run
fixture is excluded on Ubuntu because of AppArmor).

When the Chrome version in `packages/miniflare/src/index.ts` changes,
the cache key here needs to be bumped manually. A miss only triggers a
fresh download — no functional impact.

Author: petebacondarwin

.github/workflows/test-and-check.yml

@@ -136,6 +136,32 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ github.token }}
 
+      # Browser Run tests in `packages/miniflare/test/plugins/browser/index.spec.ts`
+      # and the `fixtures/browser-run` fixture use `@puppeteer/browsers` to
+      # download Chrome into the global Wrangler cache. Caching that binary
+      # across CI runs avoids ~150 MB of repeat downloads per run and reduces
+      # the surface area for the intermittent partial-extraction race that
+      # surfaces as `The browser folder (...) exists but the executable (...)
+      # is missing` (see #13971, #13980).
+      #
+      # The Browser Run fixture is skipped on Ubuntu (AppArmor), but the
+      # miniflare browser spec runs everywhere, so the cache is needed on all
+      # three OSes for `packages-and-tools` and on Windows + macOS for
+      # `fixtures`.
+      - name: Restore Chrome browser cache (Browser Run)
+        if: steps.changes.outputs.everything_but_markdown == 'true' && (matrix.suite == 'packages-and-tools' || (matrix.suite == 'fixtures' && matrix.os != 'ubuntu-latest'))
+        uses: actions/cache@v4
+        with:
+          # The Chrome version is hardcoded in `packages/miniflare/src/index.ts`
+          # (search for `browserVersion:`). Bump this key when that version
+          # changes — a cache miss only triggers a fresh download, no
+          # functional impact.
+          key: chrome-${{ runner.os }}-126.0.6478.182
+          path: |
+            ~/.cache/.wrangler/chrome
+            ~/Library/Caches/.wrangler/chrome
+            ~/AppData/Local/xdg.cache/.wrangler/chrome
+
       - name: Run tests (tools only)
         # tools _only_ needs to be tested on Linux because they're only intended to run in CI
         if: steps.changes.outputs.everything_but_markdown == 'true' && matrix.suite == 'packages-and-tools' && matrix.os == 'ubuntu-latest'