chore: add openvpn to experimental suite #345

Job	Run time
Ensure the code builds (OoniStableFullRelease)	2m 38s
Ensure the code builds (OoniStableFdroidRelease)	2m 22s
Ensure the code builds (DwStableFullRelease)	2m 32s
Ensure the code builds (DwStableFdroidRelease)	2m 19s
Run instrumented tests (25, default)	1h 2m 36s
Run unit tests	2m 30s
Archive APKs (OoniStableFullDebug)	1m 54s
Run instrumented tests (25, google_apis)	1h 2m 41s
Archive APKs (OoniStableFdroidDebug)	1m 39s
Run instrumented tests (29, default)	1h 2m 42s
Archive APKs (OoniDevFullDebug)	2m 17s
Run instrumented tests (29, google_apis)	10m 4s
Archive APKs (OoniDevFullDebugAndroidTest)	3m 3s
Archive APKs (DwStableFullDebug)	1m 40s
Archive APKs (DwStableFdroidDebug)	1m 45s
Archive APKs (DwDevFullDebug)	2m 22s
Upload artifact to Firebase App Distribution	1m 8s
	3h 46m 12s

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