chore: move the workflows off the deprecated Node 20 actions

The runners force actions/checkout@v4 and the artifact actions onto Node 24
already and warn about it on every run. Current majors instead, so the
annotation goes away and the pin says what is actually running.

.github/workflows/check.yml

@@ -11,7 +11,7 @@ jobs:
     name: syntax and shellcheck
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v7
 
       # The Makefile skips whatever is missing rather than failing, so the
       # tools it looks for have to be here or the check checks less than it