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

scripts/checksrc.pl

@@ -879,7 +879,7 @@ sub scanfile {
             }
         }
 
-        # check for "return" with parentheses around just a value/name
+        # check for "return" with parentheses around a value/name
         if($l =~ /^(.*\W)return \(\w*\);/) {
             checkwarn("RETURNPAREN", $line, length($1)+7, $file, $l,
                       "return with paren");