Update to Qt6

- New baseline minimum platform is Ubuntu 22.04
    - Qt6 requires at least 6.2
        - some deprecations may be flagged on later versions (e.g. 6.8)
    - CMake requires at least 3.22
- Include build-tests.yml github action to validate builds on mulitple platforms
- QtTest is no longer optional since it easily comes along for the ride with Qt
- Replaced QStringRef in model::SubstitutionField with simple ParserState class
- Removed deprecations up to Qt 6.2

glabels/TemplateDesigner.cpp

@@ -110,7 +110,7 @@ namespace glabels
 	/// Constructor
 	///
 	TemplateDesigner::TemplateDesigner( QWidget* parent )
-		: mIsBasedOnCopy(false), QWizard(parent)
+		: QWizard(parent)
 	{
 		setWindowTitle( tr("Product Template Designer") );
 		setPixmap( QWizard::LogoPixmap, QPixmap( ":icons/apps/48x48/glabels.svg" ) );
@@ -1315,7 +1315,7 @@ namespace glabels
 			x0Spin->setRange( x0Min, x0Max );
 			y0Spin->setRange( y0Min, y0Max );
 			dxSpin->setRange( dxMin, dxMax );
-			dySpin->setRange( dyMin, dxMax );
+			dySpin->setRange( dyMin, dyMax );
 
 			static bool alreadyInitialized = false;
 			if ( !td->isBasedOnCopy() && !alreadyInitialized )