Use ignore words file with codespell

It is not possible to automatically backport pull requests that makes
modifications to workflow files and since the codespell action has a
hard-coded list of ignored words as options, this means that any
changes to the ignored codespell words cannot be backported.

This pull request fixes this by using a ignore words file instead,
which means that adding new words does not require changing a workflow
file and hence the pull requests can be automatically backported.

.github/ignore-words

@@ -0,0 +1,4 @@
+brin
+inh
+larg
+inout

.github/workflows/code_style.yaml

@@ -66,7 +66,7 @@ jobs:
       - name: Run codespell
         run: |
           find . -type f \( -name "*.c" -or -name "*.h" -or -name "*.yaml" -or -name "*.sh" \) \
-            -exec codespell -L "brin,inh,larg,inout" {} \+
+            -exec codespell -I .github/ignore-words {} \+
 
   cc_checks:
     name: Check code formatting