Bug 573814: Update to 2021-06 branding for about dialogs (PHP package)

Not sure of the effect here, but in this area the old name of the
file was referenced. The epp.product and plugin.xml had the correct
file name.

Change-Id: I8ae1eb680b2a977c413d7f57e45c759421deb6cd

packages/org.eclipse.epp.package.php/about.ini

@@ -17,7 +17,7 @@ windowImage=eclipse16.png
 
 # Property "aboutImage" contains path to product image (500x330 or 115x164)
 # needed for primary features only
-aboutImage=eclipse_lg.gif
+aboutImage=eclipse_lg.png
 
 # Property "appName" contains name of the application (translated)
 # needed for primary features only