Update github actions to resolve most node deprecation warnings

As is github tradition, workflows started yelling about running on a
node version that was getting sunset, so here we go again.

Relevant bumps:

- https://github.com/actions/checkout/releases/tag/v4.0.0
- https://github.com/actions/setup-dotnet/releases/tag/v4.0.0
- https://github.com/actions/cache/releases/tag/v4.0.0
- https://github.com/actions/setup-java/releases/tag/v4.0.0
- https://github.com/peter-evans/create-pull-request/releases/tag/v6.0.0
- https://github.com/dorny/test-reporter/releases/tag/v1.8.0

Notably, `actions/upload-artifact` is _not_ bumped to v4, although it
should be to resolve the node deprecation warnings, because it has more
breaking changes and bumping would break `dorny/test-reporter`
(see https://github.com/dorny/test-reporter/issues/363).

.github/workflows/diffcalc.yml

@@ -140,7 +140,7 @@ jobs:
       GOOGLE_CREDS_FILE: ${{ steps.set-outputs.outputs.GOOGLE_CREDS_FILE }}
     steps:
       - name: Checkout diffcalc-sheet-generator
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           path: ${{ env.EXECUTION_ID }}
           repository: 'smoogipoo/diffcalc-sheet-generator'