fix: always respect app.json formations in scale settings

Without this change, it was possible would end up in a state where we might still try to scale processes up that no longer exists.

Closes #5205

tests/apps/python/app-5205a.json

@@ -0,0 +1,10 @@
+{
+  "formation": {
+    "web": {
+      "quantity": 1
+    },
+    "worker": {
+      "quantity": 1
+    }
+  }
+}

tests/apps/python/app-5205b.json

@@ -0,0 +1,10 @@
+{
+  "formation": {
+    "web": {
+      "quantity": 1
+    },
+    "cron": {
+      "quantity": 1
+    }
+  }
+}