tidy-up: assortment of small fixes

- examples/headerapi: fix wrong cast.
- curl_ngtcp2: delete stray character from error message.
- rustls: fix inline variable declaration.
- sendf: drop redundant `int` cast.
- libtest/cli_ws_data: drop cast with mismatched signedness.

Cherry-picked from #18343

Closes #18664

docs/examples/headerapi.c

@@ -69,7 +69,7 @@ int main(void)
       do {
         h = curl_easy_nextheader(curl, CURLH_HEADER, -1, prev);
         if(h)
-          printf(" %s: %s (%u)\n", h->name, h->value, (int)h->amount);
+          printf(" %s: %s (%u)\n", h->name, h->value, (unsigned int)h->amount);
         prev = h;
       } while(h);