github/workflows: Move codespell to a GitHub workflow, version it.

Similar to ruff.yaml, it's simpler to run the codespell command directly
from a workflow file.  And developers can run codespell directly from the
command line without the need for options, or just use pre-commit.

This commit also applies a specific version to codespell, same as
pre-commit (introduced in a166d805f4).

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

.github/workflows/code_formatting.yml

@@ -18,13 +18,3 @@ jobs:
       run: source tools/ci.sh && ci_c_code_formatting_run
     - name: Check code formatting
       run: git diff --exit-code
-
-  code-spelling:
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/checkout@v4
-    - uses: actions/setup-python@v5
-    - name: Install packages
-      run: source tools/ci.sh && ci_code_spell_setup
-    - name: Run spell checker
-      run: source tools/ci.sh && ci_code_spell_run