Bump actions/checkout to v5

The first green run carried one annotation: checkout@v4 targets Node 20,
which is deprecated, so the runner was already forcing it onto Node 24. v5
targets Node 24 natively. No behaviour change -- the fetch-depth: 0 on the
release job means the same thing -- it just stops the run from arriving with
a warning attached, which on a workflow whose whole history is "a red X that
meant nothing" is worth keeping clean.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EP9qibz6eUB3wB8sGHCVS5

Author: ralyodio

.github/workflows/release.yml

@@ -31,7 +31,7 @@ jobs:
   check:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
 
       # scripts-check skips shellcheck with a note when it is absent, so
       # without this step the lint third of the gate would quietly not run.
@@ -46,7 +46,7 @@ jobs:
     if: startsWith(github.ref, 'refs/tags/v')
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
         with: { fetch-depth: 0 }
 
       - name: Create the release