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/ws.c

@@ -1037,7 +1037,7 @@ static CURLcode ws_enc_send(struct Curl_easy *data,
      * that needs to be encoded into the buffer */
     if(buflen < ws->sendbuf_payload) {
       /* We have been called with LESS buffer data than before. This
-       * is not how it's supposed too work. */
+       * is not how it is supposed too work. */
       failf(data, "[WS] curl_ws_send() called with smaller 'buflen' than "
             "bytes already buffered in previous call, %zu vs %zu",
             buflen, ws->sendbuf_payload);