Deflake IPFS and EStargz tests

[djdongjin]

IPFS related flaky tests have the following error, e.g. in https://github.com/containerd/nerdctl/actions/runs/8412061811/job/23032444940 (error attached below)

I think the change can mitigate this flaky tests to some extends.

Also the other estargz test shouldn't be executed in parallel since it pulls and rmis a common image. (I also saw flaky related to that)

=== RUN   TestIPFS
    ipfs_linux_test.go:162: assertion failed: res.ExitCode is not exitCode: time="2024-03-24T21:11:22Z" level=fatal msg="1 errors:\nconflict: unable to delete ghcr.io/stargz-containers/alpine:3.13-org (must be forced) - image is being used by stopped container e5d04bd64e173db20d5585cd4a6376e8efa6bf6708df0d0b1859bd798c88acbf"
        
--- FAIL: TestIPFS (0.34s)
FAIL cmd/nerdctl.TestIPFS (0.34s)
=== RUN   TestIPFSAddress
    ipfs_linux_test.go:84: IPAddress=['"10.4.0.61"' ]
    ipfs_linux_test.go:87: ip address matches=["10.4.0.61" 10.4.0.61]
    ipfs_linux_test.go:162: assertion failed: res.ExitCode is not exitCode: time="2024-03-24T21:11:23Z" level=fatal msg="1 errors:\nconflict: unable to delete ghcr.io/stargz-containers/alpine:3.13-org (must be forced) - image is being used by stopped container e5d04bd64e173db20d5585cd4a6376e8efa6bf6708df0d0b1859bd798c88acbf"
        
--- FAIL: TestIPFSAddress (0.80s)
FAIL cmd/nerdctl.TestIPFSAddress (0.80s)
=== RUN   TestIPFSCommit
    ipfs_linux_test.go:162: assertion failed: res.ExitCode is not exitCode: time="2024-03-24T21:11:23Z" level=fatal msg="1 errors:\nconflict: unable to delete ghcr.io/stargz-containers/alpine:3.13-org (must be forced) - image is being used by stopped container e5d04bd64e173db20d5585cd4a6376e8efa6bf6708df0d0b1859bd798c88acbf"
        
--- FAIL: TestIPFSCommit (0.24s)
FAIL cmd/nerdctl.TestIPFSCommit (0.24s)
=== RUN   TestIPFSWithLazyPulling
    ipfs_linux_test.go:162: assertion failed: res.ExitCode is not exitCode: time="2024-03-24T21:11:24Z" level=fatal msg="1 errors:\nconflict: unable to delete ghcr.io/stargz-containers/alpine:3.13-org (must be forced) - image is being used by stopped container e5d04bd64e173db20d5585cd4a6376e8efa6bf6708df0d0b1859bd798c88acbf"

[AkihiroSuda]

Thanks