Force 32bit values for size serialization

This restores compatibility with Qt 5 data and fixes the mail serializer
unit test with Qt 6.

.kde-ci.yml

@@ -9,4 +9,4 @@ Dependencies:
     'pim/kmime' : '@same'
 
 Options:
-  require-passing-tests-on: [ 'Linux/Qt5', 'FreeBSD/Qt5' ]
+  require-passing-tests-on: [ 'Linux', 'FreeBSD' ]

serializers/akonadi_serializer_mail.cpp

@@ -211,7 +211,7 @@ template<typename T>
 static void serializeAddrList(QDataStream &stream, T *hdr)
 {
     const KMime::Types::Mailbox::List mb = hdr->mailboxes();
-    stream << mb.size();
+    stream << (qint32)mb.size();
     for (const KMime::Types::Mailbox &mbox : mb) {
         stream << mbox.name() << mbox.addrSpec().localPart << mbox.addrSpec().domain;
     }