CI: extend spellchecker whitelist

let us ignore *.pem files
diff --git a/.github/workflows/codespell.yml b/.github/workflows/codespell.yml
index 9a630cf..c706c4e 100644
--- a/.github/workflows/codespell.yml
+++ b/.github/workflows/codespell.yml
@@ -14,4 +14,4 @@
     - name: install prerequisites
       run: sudo pip install codespell
     - name: check
-      run: codespell -c -q 2 --ignore-words-list ist,hist,wan,ca,cas,que,ans --skip="CHANGELOG,*.fig"
+      run: codespell -c -q 2 --ignore-words-list ist,hist,wan,ca,cas,que,ans --skip="CHANGELOG,*.fig,*.pem"