badwords: check indented lines in source code, fix fallouts

- badwords.pl: add `-a` option to check all lines in source code files.
  Before this patch indented lines were skipped (to avoid Markdown code
  fences.)
- GHA/checksrc: use `-a` when verifying the source code.
- GHA/checksrc: disable `So` and `But` rules for source code.
- GHA/checksrc: add docs/examples to the verified sources.
- badwords.txt: delete 4 duplicates.
- badwords.txt: group and sort contractions.
- badwords.txt: allow ` url = `, `DIR`, `<file name`.

Closes #19536

lib/hsts.c

@@ -277,7 +277,7 @@ struct stsentry *Curl_hsts(struct hsts *h, const char *hostname,
           blen = ntail;
         }
       }
-      /* avoid curl_strequal because the host name is not null-terminated */
+      /* avoid curl_strequal because the hostname is not null-terminated */
       if((hlen == ntail) && curl_strnequal(hostname, sts->host, hlen))
         return sts;
     }