Bump pinned botorch to 0.9.4 (#1987)

Summary:
Pull Request resolved: #1987

Preparing to release Ax 0.3.5

Reviewed By: saitcakmak

Differential Revision: D51268927

fbshipit-source-id: 4ed701c51d69bec77a219256675447b5bad3b316

setup.py

@@ -9,7 +9,7 @@
 from setuptools import find_packages, setup
 
 # TODO: read pinned Botorch version from a shared source
-PINNED_BOTORCH_VERSION = "0.9.2"
+PINNED_BOTORCH_VERSION = "0.9.4"
 
 if os.environ.get("ALLOW_BOTORCH_LATEST"):
     # allows a more recent previously installed version of botorch to remain