Unify access to env variables #143

Job	Run time
generate-matrix	2s
test-recipes (custom_environment.dockerfile, ubuntu-latest)	1m 9s
test-recipes (custom_environment.dockerfile, ARM64)	57s
test-recipes (dask_jupyterlab.dockerfile, ubuntu-latest)	43s
test-recipes (dask_jupyterlab.dockerfile, ARM64)	26s
test-recipes (jupyterhub_version.dockerfile, ubuntu-latest)	34s
test-recipes (jupyterhub_version.dockerfile, ARM64)	5s
test-recipes (mamba_install.dockerfile, ubuntu-latest)	45s
test-recipes (mamba_install.dockerfile, ARM64)	4s
test-recipes (manpage_install.dockerfile, ubuntu-latest)	51s
test-recipes (manpage_install.dockerfile, ARM64)	58s
test-recipes (microsoft_odbc.dockerfile, ubuntu-latest)	45s
test-recipes (microsoft_odbc.dockerfile, ARM64)	1m 1s
test-recipes (oracledb.dockerfile, ubuntu-latest)	2m 10s
test-recipes (pip_install.dockerfile, ubuntu-latest)	27s
test-recipes (pip_install.dockerfile, ARM64)	10s
test-recipes (rise_jupyterlab.dockerfile, ubuntu-latest)	32s
test-recipes (rise_jupyterlab.dockerfile, ARM64)	5s
test-recipes (spellcheck_notebook_v6.dockerfile, ubuntu-latest)	29s
test-recipes (spellcheck_notebook_v6.dockerfile, ARM64)	4s
test-recipes (xgboost.dockerfile, ubuntu-latest)	35s
test-recipes (xgboost.dockerfile, ARM64)	20s
	13m 12s

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