Fix env variable loading in Cost Benchmark workflow #28574

Job	Run time
Check GCP variables	15s
Python Wordcount Direct Runner (self-hosted, ubuntu-20.04, main, 3.9)	8m 26s
Python Unit Tests (macos-latest, 3.9, py39)	17m 59s
Python Wordcount Direct Runner (self-hosted, ubuntu-20.04, main, 3.10)	7m 34s
Python Unit Tests (macos-latest, 3.10, py310)	15m 33s
Python Wordcount Direct Runner (self-hosted, ubuntu-20.04, main, 3.11)	6m 49s
Python Unit Tests (macos-latest, 3.11, py311)	15m 3s
Python Wordcount Direct Runner (self-hosted, ubuntu-20.04, main, 3.12)	6m 49s
Python Unit Tests (macos-latest, 3.12, py312)	14m 23s
Python Wordcount Direct Runner (macos-latest, 3.9)	3m 35s
Python Unit Tests (windows-latest, 3.9, py39)	15m 5s
Python Wordcount Direct Runner (macos-latest, 3.10)	3m 24s
Python Unit Tests (windows-latest, 3.10, py310)	17m 4s
Python Wordcount Direct Runner (macos-latest, 3.11)	2m 44s
Python Unit Tests (windows-latest, 3.11, py311)	14m 17s
Python Wordcount Direct Runner (macos-latest, 3.12)	2m 30s
Python Unit Tests (windows-latest, 3.12, py312)	15m 5s
Python Wordcount Direct Runner (windows-latest, 3.9)	3m 46s
Python Wordcount Direct Runner (windows-latest, 3.10)	3m 47s
Python Wordcount Direct Runner (windows-latest, 3.11)	5m 12s
Python Wordcount Direct Runner (windows-latest, 3.12)	3m 25s
Build python source distribution	0s
Python Wordcount Dataflow	0s
	3h 2m 45s

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