Bump target PHP version to 8.3

This makes phan complain when someone uses functionality that is not
compatible with PHP 8.3 (mostly deprecated functionality), where an
alternative exists in the minimum supported PHP version (7.4).

Change-Id: I01b2049beb0d6a9212861bd971888c49d0367015

src/base-config-functions.php

@@ -64,7 +64,7 @@ function setBaseOptions( string $curDir, ConfigBuilder $configBuilder ): void {
 		->readClassAliases( true )
 		->enableRedundantConditionDetection( true )
 		->setMinimumPHPVersion( '7.4' )
-		->setTargetPHPVersion( '8.1' )
+		->setTargetPHPVersion( '8.3' )
 		->addPlugins( [
 			'PregRegexCheckerPlugin',
 			'UnusedSuppressionPlugin',