Ignore test failures since tests time out on armhf

Tests fail on armhf only:

=== RUN   TestOpaqueKeyRoundtripJWE
panic: test timed out after 10m0s

goroutine 105 [running]:
testing.(*M).startAlarm.func1()
        /usr/lib/go-1.15/src/testing/testing.go:1618 +0xbc
created by time.goFunc
        /usr/lib/go-1.15/src/time/sleep.go:167 +0x34

goroutine 1 [chan receive]:
testing.(*T).Run(0x2102380, 0x3180ee, 0x19, 0x33f724, 0x401)
        /usr/lib/go-1.15/src/testing/testing.go:1169 +0x240
testing.runTests.func1(0x1c00ee0)
        /usr/lib/go-1.15/src/testing/testing.go:1439 +0x68
testing.tRunner(0x1c00ee0, 0x1d35ed8)
        /usr/lib/go-1.15/src/testing/testing.go:1123 +0xc8
testing.runTests(0x1f9c7e0, 0x51a1a8, 0x73, 0x73, 0x357879cb, 0xc015a3d8, 0x9adc7beb, 0x8d, 0x51c620, 0x1cbe230)
        /usr/lib/go-1.15/src/testing/testing.go:1437 +0x268
testing.(*M).Run(0x1cbe230, 0x0)
        /usr/lib/go-1.15/src/testing/testing.go:1345 +0x16c
main.main()
        _testmain.go:593 +0x120

See Debian bug #986916.