ci: skip ./api/vendor in codespell runs

The `./api/vendor` directory seems to have spellcheck problems while
running locally. For some reason the CI jobs running in GitHub do not
seem to be affected.

Signed-off-by: Niels de Vos <ndevos@ibm.com>

scripts/codespell.conf

@@ -1,5 +1,5 @@
 [codespell]
 # TODO: enable codespell on retest folder except vendor
-skip = .git,./vendor,./docs/design/proposals/images,./actions/retest/*,go.sum
+skip = .git,./vendor,./docs/design/proposals/images,./actions/retest/*,./api/vendor,go.sum
 ignore-words-list = ExtraVersion,extraversion,ba
 check-filenames = true