misc: fix spelling in docs and comments

also: remove outdated sentence

Closes #9644

docs/cmdline-opts/header.d

@@ -16,7 +16,7 @@ Extra header to include in information sent. When used within an HTTP request,
 it is added to the regular request headers.
 
 For an IMAP or SMTP MIME uploaded mail built with --form options, it is
-prepended to the resulting MIME document, effectively incuding it at the mail
+prepended to the resulting MIME document, effectively including it at the mail
 global level. It does not affect raw uploaded mails (Added in 7.56.0).
 
 You may specify any number of extra headers. Note that if you should add a

lib/urlapi.c

@@ -781,9 +781,6 @@ static CURLUcode decode_host(struct dynbuf *host)
  * The function handles a query part ('?' + stuff) appended but it expects
  * that fragments ('#' + stuff) have already been cut off.
  *
- * Note that this funciton *writes* a byte into the source buffer during its
- * operation.
- *
  * RETURNS
  *
  * an allocated dedotdotified output string

tests/manpage-syntax.pl

@@ -167,7 +167,7 @@ sub scanmanpage {
             my ($pre, $format) = ($1, $2);
             if($pre !~ /\\\z/) {
                 # only if there wasn't another backslash before the \f
-                print STDERR "$file:$line suspicios \\f format!\n";
+                print STDERR "$file:$line suspicious \\f format!\n";
                 $errors++;
             }
         }