Cirrus: skip BuildKit tests

[AkihiroSuda]

#622 is too much flaky

[AkihiroSuda]

Still too much flaky

== CONT  TestRunVolume
--- PASS: TestRunTmpfs (0.91s)
=== CONT  TestRunAnonymousVolume
--- PASS: TestRunAnonymousVolume (0.48s)
=== CONT  TestBuildFromStdin
    testutil.go:376: buildkitHost="unix:///run/user/1000/buildkit/buildkitd.sock"
time="2022-01-26T08:44:47Z" level=error msg="error: failed to list workers: Unavailable: connection error: desc = \"transport: error while dialing: dial unix /run/user/1000/buildkit/buildkitd.sock: connect: no such file or directory\"\n"
    testutil.go:378: test requires buildkitd: `buildctl` needs to be installed and `buildkitd` needs to be running, see https://github.com/moby/buildkit , and `containerd-rootless-setuptool.sh install-buildkit`: exit status 1
--- SKIP: TestBuildFromStdin (0.02s)
=== CONT  TestRunUlimit
=== CONT  TestRunVolume
    run_mount_linux_test.go:64: assertion failed: expression is false: res.ExitCode == exitCode: time="2022-01-26T08:44:48Z" level=warning msg="failed to delete task f90eb47315e73c8cda58e736299cde856d8aa753a739a9eb80440c04d1673568" error="unknown error after kill: runc did not terminate successfully: exit status 1: lstat /sys/fs/cgroup/user.slice/user-1000.slice/[email protected]/user.slice/nerdctl-f90eb47315e73c8cda58e736299cde856d8aa753a739a9eb80440c04d1673568.scope: no such file or directory\n: unknown"
        time="2022-01-26T08:44:48Z" level=warning msg="failed to remove container \"f90eb47315e73c8cda58e736299cde856d8aa753a739a9eb80440c04d1673568\"" error="cannot delete running task f90eb47315e73c8cda58e736299cde856d8aa753a739a9eb80440c04d1673568: failed precondition"
        time="2022-01-26T08:44:48Z" level=warning msg="failed to remove container \"f90eb47315e73c8cda58e736299cde856d8aa753a739a9eb80440c04d1673568\"" error="cannot delete running task f90eb47315e73c8cda58e736299cde856d8aa753a739a9eb80440c04d1673568: failed precondition"
        time="2022-01-26T08:44:48Z" level=warning msg="failed to release name store for container \"f90eb47315e73c8cda58e736299cde856d8aa753a739a9eb80440c04d1673568\"" error="cannot delete running task f90eb47315e73c8cda58e736299cde856d8aa753a739a9eb80440c04d1673568: failed precondition"
        time="2022-01-26T08:44:48Z" level=fatal msg="cannot delete running task f90eb47315e73c8cda58e736299cde856d8aa753a739a9eb80440c04d1673568: failed precondition"
--- FAIL: TestRunVolume (1.29s)
=== CONT  TestRunUserGID/#00
--- PASS: TestCommit (2.66s)
=== CONT  TestRunUserGID/guest
=== CONT  TestWait
    wait_test.go:45: assertion failed: error is not nil: expected "0\n0\n123\n", got "0\n123\n0\n": 0
        123
        0
--- FAIL: TestWait (6.36s)
=== CONT  TestRunUserGID/nobody

https://cirrus-ci.com/task/6732955237220352?logs=rootless_test#L709