CI: pin moto to 1.3.4 (pandas-dev#22959)

Author: TomAugspurger

ci/travis-27.yaml

@@ -44,7 +44,7 @@ dependencies:
   # universal
   - pytest
   - pytest-xdist
-  - moto
+  - moto==1.3.4
   - hypothesis>=3.58.0
   - pip:
     - backports.lzma