chore(CI): Adjust testing matrix for Nextcloud 34 on stable34

Signed-off-by: Joas Schilling <coding@schilljs.com>

Author: nickvergessen

composer.json

@@ -34,7 +34,7 @@
 	},
 	"require-dev": {
 		"bamarni/composer-bin-plugin": "^1.8",
-		"nextcloud/ocp": "dev-master"
+		"nextcloud/ocp": "dev-stable34"
 	},
 	"extra": {
 		"bamarni-bin": {