Fix env variable loading in Cost Benchmark workflow #28576

Job	Run time
Check GCP variables	17s
Python Unit Tests (macos-latest, 3.9, py39)	14m 6s
Python Unit Tests (macos-latest, 3.10, py310)	15m 5s
Python Unit Tests (macos-latest, 3.11, py311)	16m 1s
Python Unit Tests (macos-latest, 3.12, py312)	16m 1s
Python Unit Tests (windows-latest, 3.9, py39)	13m 57s
Python Unit Tests (windows-latest, 3.10, py310)	14m 42s
Python Unit Tests (windows-latest, 3.11, py311)	14m 37s
Python Wordcount Direct Runner (self-hosted, ubuntu-20.04, main, 3.9)	6m 37s
Python Unit Tests (windows-latest, 3.12, py312)	14m 34s
Python Wordcount Direct Runner (self-hosted, ubuntu-20.04, main, 3.10)	10m 35s
Python Wordcount Direct Runner (self-hosted, ubuntu-20.04, main, 3.11)	8m 21s
Python Wordcount Direct Runner (self-hosted, ubuntu-20.04, main, 3.12)	10m 26s
Python Wordcount Direct Runner (macos-latest, 3.9)	2m 44s
Python Wordcount Direct Runner (macos-latest, 3.10)	2m 41s
Python Wordcount Direct Runner (macos-latest, 3.11)	2m 31s
Python Wordcount Direct Runner (macos-latest, 3.12)	2m 35s
Python Wordcount Direct Runner (windows-latest, 3.9)	4m 2s
Python Wordcount Direct Runner (windows-latest, 3.10)	3m 16s
Python Wordcount Direct Runner (windows-latest, 3.11)	3m 1s
Python Wordcount Direct Runner (windows-latest, 3.12)	4m 1s
Build python source distribution	0s
Python Wordcount Dataflow	0s
	3h 0m 10s

Provide feedback