create_release_tasks.pl: explicitly dereference arguments to 'keys'

Being able to pass a scalar to e.g. keys was an experimental feature
that was added in Perl 5.14 and since declared failed, thus causing the
script to fail with an "Experimental keys on scalar is now forbidden"
error.

misc-scripts/jira/create_release_tasks.pl

@@ -253,7 +253,7 @@ sub validate_parameters {
 	  $parameters->{config} );
 
   print "Dates:\n";
-  foreach my $date_label (keys $parameters->{dates}) {
+  foreach my $date_label (keys %{$parameters->{dates}}) {
       printf( "%33s: %s\n",
 	      $date_label,
 	      $parameters->{dates}->{$date_label} );
@@ -513,7 +513,7 @@ sub replace_placeholders {
       }
   }
 
-  for my $param (keys $parameters->{dates}) {
+  for my $param (keys %{$parameters->{dates}}) {
       if($line =~ /<$param>/) {
 	  $line =~ s/<$param>/$parameters->{dates}->{$param}/eg;
       }
@@ -693,7 +693,7 @@ sub fetch_dates {
 
   my $events = $hash->{events};
 
-  foreach my $milestone_name (keys $parameters->{ical}) {
+  foreach my $milestone_name (keys %{$parameters->{ical}}) {
       my $calendar_label = $parameters->{ical}->{$milestone_name};
       $calendar_label = replace_placeholders($calendar_label, $parameters);
       print "Looking for '$calendar_label' in ical...";
@@ -730,9 +730,9 @@ sub find_event_by_name {
   my ( $label, $events ) = @_;
 
   foreach my $year (keys %$events) {
-      foreach my $month (keys $events->{$year}) {
-	  foreach my $day (keys $events->{$year}->{$month}) {
-	      foreach my $event (keys $events->{$year}->{$month}->{$day} ) {
+      foreach my $month (keys %{$events->{$year}}) {
+	  foreach my $day (keys %{$events->{$year}->{$month}}) {
+	      foreach my $event (keys %{$events->{$year}->{$month}->{$day}} ) {
 		  if($events->{$year}->{$month}->{$day}->{$event}->{SUMMARY} eq $label) {
 		      return $events->{$year}->{$month}->{$day}->{$event};
 		  }