tidy-up: miscellaneous

- drop more uses of the word "just". (not enforced here)
- drop some uses of the "will" word.
- "then" -> "than".
- tests/http/testenv/curl.py: fix copy-paste typo in error message.
- pytest: replace `shutdownh` with `shutdown` in test names.
  Spotted by GitHub Code Quality.
- comment typos.
- whitespace and newlines fixes.

Closes #21830

lib/urlapi.c

@@ -480,7 +480,7 @@ static CURLUcode hostname_check(struct Curl_URL *u, char *hostname,
       /* more than one trailing dot is not allowed */
       return CURLUE_BAD_HOSTNAME;
     else if((hlen == 1) && (hostname[0] == '.'))
-      /* just a single dot is not allowed */
+      /* a single dot alone is not allowed */
       return CURLUE_BAD_HOSTNAME;
   }
   return CURLUE_OK;