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/multi_ev.c

@@ -340,7 +340,7 @@ static CURLMcode mev_pollset_diff(struct Curl_multi *multi,
     /* What was the previous action the transfer had regarding this socket?
      * If the transfer is new to the socket, disregard the information
      * in `last_poll`, because the socket might have been destroyed and
-     * reopened. We'd have cleared the sh_entry for that, but the socket
+     * reopened. We would have cleared the sh_entry for that, but the socket
      * might still be mentioned in the hashed pollsets. */
     last_action = 0;
     if(first_time) {