Exclude third_party from spell checker

.github/workflows/codespell.yml

@@ -14,5 +14,5 @@ jobs:
       - uses: codespell-project/actions-codespell@master
         with:
           check_filenames: true
-          skip: ./.git,./conformance/third_party,*.snk,*.pb,*.pb.cc,*.pb.h,./src/google/protobuf/testdata,./objectivec/Tests,./python/compatibility_tests/v2.5.0/tests/google/protobuf/internal,./.github/workflows/codespell.yml
+          skip: ./.git,./third_party,./conformance/third_party,*.snk,*.pb,*.pb.cc,*.pb.h,./src/google/protobuf/testdata,./objectivec/Tests,./python/compatibility_tests/v2.5.0/tests/google/protobuf/internal,./.github/workflows/codespell.yml
           ignore_words_list: "alow,alse,ba,chec,cleare,copyable,cloneable,dedup,dur,errorprone,falsy,files',fo,fundementals,hel,importd,inout,leapyear,nd,nin,ois,ons,parseable,process',ro,te,testof,ue,unparseable,wasn,wee,gae,keyserver,objext,od,optin,streem,sur,falsy"