fix: Normalize openai client stop reason to make more robust #3390

Job	Run time
format	59s
mypy (./packages/autogen-core)	2m 59s
lint	55s
mypy (./packages/autogen-magentic-one)	1m 21s
mypy (./packages/agbench)	1m 25s
pyright (./packages/autogen-core)	55s
mypy (./packages/autogen-ext)	1m 51s
pyright (./packages/autogen-magentic-one)	1m 8s
mypy (./packages/autogen-agentchat)	1m 21s
pyright (./packages/agbench)	1m 7s
pyright (./packages/autogen-ext)	1m 28s
mypy (./packages/magentic-one-cli)	1m 17s
pyright (./packages/autogen-agentchat)	1m 14s
pyright (./packages/magentic-one-cli)	53s
check-proto-changes-python	1m 3s
codecov (./packages/autogen-core)	1m 0s
codecov (./packages/autogen-magentic-one)	1m 49s
docs (./packages/autogen-core)	1m 39s
docs-example-check (./packages/autogen-core)	2m 51s
codecov (./packages/autogen-ext)	2m 59s
codecov (./packages/autogen-agentchat)	1m 1s
markdown-code-lint	2m 28s
samples-code-check	1m 28s
test (./packages/autogen-core)	1m 2s
test (./packages/autogen-magentic-one)	1m 20s
test (./packages/autogen-ext)	2m 45s
test (./packages/autogen-agentchat)	1m 10s
	41m 28s

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