Fix perl script warning

The apache logs are filled with warnings about this when it's used.

https://blog.gerv.net/2014/10/new-class-of-vulnerability-in-perl-web-applications/

Change-Id: I977d2b022d706d9587c033fd8e80f129e60c439c
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

tests/testserver/apache2/testdata/www/cgi-bin/multipart.cgi

@@ -11,7 +11,7 @@ print "content type: $contentType\n";
 
 if ($contentType =~ /^multipart\/form-data/) {
     foreach my $key ($q->param) {
-        foreach my $value ($q->param($key)) {
+        foreach my $value (scalar $q->param($key)) {
             if ($key =~ /text/) {
                 $retValue = $value;
             } else {