Try using Python 3 for codespell

Running it using Python 2 seems to result in a problem with not matching
an exclusion line with non-ASCII character, which works fine with Python
3 locally.

.github/workflows/code_checks.yml

@@ -36,7 +36,7 @@ jobs:
 
       - name: Install codespell
         run: |
-          pip install --no-warn-script-location codespell==1.17.1
+          pip3 install --no-warn-script-location codespell==1.17.1
 
       - name: Run codespell
         run: |