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/fake_addrinfo.c

@@ -180,7 +180,7 @@ int r_getaddrinfo(const char *node,
         curl_mfprintf(stderr, "ares_set_servers_ports_csv failed: %d", rc);
         /* Cleanup */
         ares_destroy(channel);
-        return EAI_MEMORY; /* we can't run */
+        return EAI_MEMORY; /* we cannot run */
       }
     }
   }