Fix env variable loading in Cost Benchmark workflow #30864

Job	Run time
Build python source distribution	59s
Check environment variables	15s
Prepare GCS	0s
Build python cp39- wheels on auto for ubuntu-20.04	22m 28s
Build python cp310- wheels on auto for ubuntu-20.04	22m 7s
Build python cp311- wheels on auto for ubuntu-20.04	23m 8s
Build python cp312- wheels on auto for ubuntu-20.04	22m 46s
Build python cp39- wheels on auto for macos-13	21s
Build python cp310- wheels on auto for macos-13	19s
Build python cp311- wheels on auto for macos-13	18s
Build python cp312- wheels on auto for macos-13	3m 14s
Build python cp39- wheels on auto for windows-latest	23s
Build python cp310- wheels on auto for windows-latest	18s
Upload python source distribution to GCS bucket	0s
Build python cp311- wheels on auto for windows-latest	20s
Build python cp312- wheels on auto for windows-latest	5m 39s
Build python cp39- wheels on aarch64 for ubuntu-20.04	50s
Build python cp310- wheels on aarch64 for ubuntu-20.04	32s
Build python cp311- wheels on aarch64 for ubuntu-20.04	54s
Build python cp312- wheels on aarch64 for ubuntu-20.04	38m 27s
Branch repo nightly	1s
Upload wheels to GCS bucket	1s
List files on Google Cloud Storage Bucket	1s
	2h 23m 21s

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