Properly unset proxy env if empty #4339

Job	Run time
Ruby analysis (macos-latest, linked)	1m 10s
Ruby analysis (ubuntu-latest, default)	45s
Ruby analysis (macos-latest, nightly-latest)	59s
Ruby analysis (ubuntu-latest, linked)	45s
Ruby analysis (macos-latest, default)	1m 13s
Ruby analysis (ubuntu-latest, nightly-latest)	46s
	5m 38s

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