[ci] Shorten max steps for strikergoalie (#4394)

config/ppo/StrikersVsGoalie.yaml

         gamma: 0.99
         strength: 1.0
     keep_checkpoints: 5
-    max_steps: 50000000
+    max_steps: 30000000
     time_horizon: 1000
     summary_freq: 10000
     threaded: true