games/valheim: always update on startup

This has already been deployed to prod.

Change-Id: I02896bd7d12d89630b0465365e08a8980738184d
diff --git a/games/valheim/prod.jsonnet b/games/valheim/prod.jsonnet
index 6c10b8b..1ec9409 100644
--- a/games/valheim/prod.jsonnet
+++ b/games/valheim/prod.jsonnet
@@ -124,6 +124,8 @@
                                         PUBLIC: "1",
                                         PASSWORD: kube.SecretKeyRef(game.secret, "public"),
                                         NAME: cfg.displayName,
+                                        # Always attempt to update valheim on startup.
+                                        FORCE_INSTALL: "1",
                                     },
                                     resources: {
                                         requests: {