Adjust .codespellrc

- add 'external/*' to the list of patterns to skip
- add '*.csr' to the list of patterns to skip

Reviewed-by: Norbert Pocs <norbertp@openssl.org>
Reviewed-by: Nikola Pajkovsky <nikolap@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/29437)

.codespellrc

@@ -332,6 +332,7 @@ skip =
     *.asc,
     *.bin,
     *.crt,
+    *.csr,
     *.css.map,
     *.eps,
     *.fr.utf-8,
@@ -441,6 +442,7 @@ skip =
     CREDITS,
     CREDITS.TXT,
     DONATIONS,
+    external/*,
     jquery.js,
     jquery.min.map,
     localization*-[a-z][a-z]_[a-zA-Z][a-zA-Z].*,