[skip ci] update screenshot url in metainfo file

dist/linux/common/org.cryptomator.Cryptomator.metainfo.xml

@@ -48,7 +48,7 @@
 		</screenshot>
 		<screenshot>
 			<caption>Dark theme available</caption>
-			<image>https://static.cryptomator.org/desktop/flathubScreenshots/MainWindowUnlock_dark.png</image>
+			<image>https://static.cryptomator.org/desktop/flathubScreenshots/MainWindowUnlocked_dark.png</image>
 		</screenshot>
 		<screenshot>
 			<caption>Uses AES-GCM 256 - an industry standardized, quantum resistant encryption</caption>