chore: add openvpn to experimental suite #343

Job	Run time
Ensure the code builds (OoniStableFullRelease)	2m 32s
Ensure the code builds (OoniStableFdroidRelease)	2m 32s
Ensure the code builds (DwStableFullRelease)	2m 37s
Ensure the code builds (DwStableFdroidRelease)	2m 27s
Run instrumented tests (25, default)	4m 35s
Run unit tests	1m 58s
Archive APKs (OoniStableFullDebug)	1m 6s
Run instrumented tests (25, google_apis)	4m 34s
Archive APKs (OoniStableFdroidDebug)	1m 6s
Run instrumented tests (29, default)	4m 34s
Archive APKs (OoniDevFullDebug)	1m 8s
Run instrumented tests (29, google_apis)	4m 28s
Archive APKs (OoniDevFullDebugAndroidTest)	47s
Archive APKs (DwStableFullDebug)	1m 7s
Archive APKs (DwStableFdroidDebug)	1m 8s
Archive APKs (DwDevFullDebug)	1m 6s
Upload artifact to Firebase App Distribution	0s
	37m 45s

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