CI: Update actions/cache to v3

This version now natively supports read-only caches (`cache/restore@v3`)
so we no longer need to pin the version to a commit in actions/cache#489
which is an unmerged PR.

The update is mostly mechanical:
- Steps with `CACHE_SKIP_SAVE` not set can use the plain `cache@v3`
  action.
- Steps with `CACHE_SKIP_SAVE` set to a constant `true` are changed to
  `cache/restore@v3`.
- Steps with saving disabled when running on a pull request are changed
  to a pair of `cache/restore@v3` and `cache/save@v3`. This setup is
  used for the large (100s of MB) ccache and Toolchain caches. As caches
  saved in pull requests can only be utilized from within the same PR,
  uploading these would only waste time and our storage quote.
  Therefore, we skip the `save` steps if running on a PR.

Co-authored-by: Cameron Youell <cameronyouell@gmail.com>

.github/workflows/serenity-js-artifacts.yml

@@ -60,22 +60,19 @@ jobs:
           mkdir -p Build/CLDR
 
       - name: TimeZoneData cache
-        # TODO: Change the version to the released version when https://github.com/actions/cache/pull/489 (or 571) is merged.
-        uses: actions/cache@03e00da99d75a2204924908e1cca7902cafce66b
+        uses: actions/cache@v3
         with:
           path: ${{ github.workspace }}/libjs-test262/Build/TZDB
           key: TimeZoneData-${{ hashFiles('Meta/CMake/time_zone_data.cmake') }}
 
       - name: UnicodeData cache
-        # TODO: Change the version to the released version when https://github.com/actions/cache/pull/489 (or 571) is merged.
-        uses: actions/cache@03e00da99d75a2204924908e1cca7902cafce66b
+        uses: actions/cache@v3
         with:
           path: ${{ github.workspace }}/libjs-test262/Build/UCD
           key: UnicodeData-${{ hashFiles('Meta/CMake/unicode_data.cmake') }}
 
       - name: UnicodeLocale cache
-        # TODO: Change the version to the released version when https://github.com/actions/cache/pull/489 (or 571) is merged.
-        uses: actions/cache@03e00da99d75a2204924908e1cca7902cafce66b
+        uses: actions/cache@v3
         with:
           path: ${{ github.workspace }}/libjs-test262/Build/CLDR
           key: UnicodeLocale-${{ hashFiles('Meta/CMake/locale_data.cmake') }}