CI: github: add a few more words to the codespell ignore list

This adds "referer,ot,uint,iif,fo,keep-alives" to the ignore list:
  - "referer" is the well-known HTTP header field name (with its
    spelling error)
  - "ot" appears a lot in the opentracing contrib.
  - "iff" often stands for "if and only if"
  - "fo" appears as a test string in tests/ist.c (could possibly be
     changed)
  - "keep-alives" appears as a noon in "...enable TCP keep-alives".
diff --git a/.github/workflows/codespell.yml b/.github/workflows/codespell.yml
index c752591..8029a21 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,te,nd --skip="CHANGELOG,*.fig,*.pem"
+      run: codespell -c -q 2 --ignore-words-list ist,hist,wan,ca,cas,que,ans,te,nd,referer,ot,uint,iif,fo,keep-alives --skip="CHANGELOG,*.fig,*.pem"