Revert "Remove conditional for pypy (#130)"

This reverts commit 0fc8967.

it turns out the pypy step is GLACIAL

Author: richvdh

synapse/pipeline.yml

@@ -287,6 +287,7 @@ steps:
   #    This step is allowed to fail
 
   - label: ":python: PyPy3.6"
+    if: "build.message =~ /pypy/i"
     soft_fail: true
     command:
       # No *trial_setup due to docker-library/pypy#52