Fix: Properly await `agent.run()` in README `Hello World` example #3356

Job	Run time
format	56s
lint	45s
mypy (./packages/autogen-core)	2m 5s
pyright (./packages/autogen-core)	1m 5s
mypy (./packages/autogen-magentic-one)	1m 4s
pyright (./packages/autogen-magentic-one)	1m 5s
test (./packages/autogen-core)	50s
mypy (./packages/agbench)	51s
test (./packages/autogen-magentic-one)	1m 21s
pyright (./packages/agbench)	1m 17s
mypy (./packages/autogen-ext)	1m 44s
test (./packages/autogen-ext)	2m 44s
pyright (./packages/autogen-ext)	1m 5s
mypy (./packages/autogen-agentchat)	1m 4s
test (./packages/autogen-agentchat)	1m 12s
pyright (./packages/autogen-agentchat)	1m 2s
mypy (./packages/magentic-one-cli)	1m 4s
pyright (./packages/magentic-one-cli)	1m 0s
check-proto-changes-python	1m 23s
codecov (./packages/autogen-core)	56s
docs (./packages/autogen-core)	1m 33s
codecov (./packages/autogen-magentic-one)	1m 46s
codecov (./packages/autogen-ext)	2m 40s
codecov (./packages/autogen-agentchat)	1m 11s
docs-example-check (./packages/autogen-core)	2m 41s
markdown-code-lint	2m 11s
samples-code-check	1m 3s
	37m 38s

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