ci: Add missing environment variable to integration-test #100

Job	Run time
Compatibility test	4m 47s
Swift 6 Language Mode	0s
Example packages / Linux (5.8)	22s
Example packages / Linux (5.9)	16m 13s
Example packages / Linux (5.10)	15m 43s
Example packages / Linux (nightly-6.0)	21m 42s
Example packages / Linux (nightly-main)	26s
Integration test / Linux (5.8)	22s
Integration test / Linux (5.9)	1m 32s
Integration test / Linux (5.10)	1m 38s
Integration test / Linux (nightly-6.0)	2m 12s
Integration test / Linux (nightly-main)	26s
Soundness / API breakage check	2m 40s
Soundness / Documentation check	1m 45s
Soundness / Unacceptable language check	4s
Soundness / License headers check	6s
Soundness / Broken symlinks check	3s
Soundness / Format check	36s
Soundness / Shell check	29s
Unit tests / Unit tests / Linux (5.8)	21s
Unit tests / Unit tests / Linux (5.9)	1m 31s
Unit tests / Unit tests / Linux (5.10)	1m 32s
Unit tests / Unit tests / Linux (nightly-6.0)	2m 4s
Unit tests / Unit tests / Linux (nightly-main)	26s
	1h 17m 0s

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