Pin httpx version for openai v1.7.2 (#1269)

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Author: umaannamalai

tox.ini

@@ -377,6 +377,7 @@ deps =
     framework_tornado-tornadomaster: https://github.com/tornadoweb/tornado/archive/master.zip
     mlmodel_openai-openai0: openai[datalib]<1.0
     mlmodel_openai-openai107: openai[datalib]<1.8
+    mlmodel_openai-openai107: httpx<0.28
     mlmodel_openai-openailatest: openai[datalib]
     ; Required for openai testing
     mlmodel_openai: protobuf