[CSI unit tests] TestGetVolumeStatCapabilitiesWithoutVmMode is broken

[aikuchin]

When it runs separately from other tests in the suite it fails:

./ya test -tt -r ./cloud/blockstore/tools/csi_driver/internal/driver/node.go --add-protobuf-result -P --test-filter='tests::TestGetVolumeStatCapabilitiesWithoutVmMode'
Warn: cloud/blockstore/tools/csi_driver/internal/driver/node.go is not a buildable target. Skip it.
------- [TS] {default-linux-x86_64, release} cloud/blockstore/tools/csi_driver/internal/driver/tests/tests >> tests::TestGetVolumeStatCapabilitiesWithoutVmMode
Test command err:
2024/09/23 06:07:06 csi.NodeGetVolumeStats: volume_id:"test-disk-id-42" volume_path:"/home/antonkuchin/.ya/build/build_root/6ro4/000193/r3tmp/pods/test-pod-id-13/volumes/test-disk-id-42/mount"
Number of suites skipped by name: 2, by filter tests::TestGetVolumeStatCapabilitiesWithoutVmMode

cloud/blockstore/tools/csi_driver/internal/driver/tests <go_test>
------ sole chunk ran 1 test (total:2.01s - setup:0.01s test:1.94s)
[fail] tests::TestGetVolumeStatCapabilitiesWithoutVmMode [default-linux-x86_64-release] (0.00s)
node_test.go:686: 
          Error Trace:  /-S/cloud/blockstore/tools/csi_driver/internal/driver/node_test.go:686
          Error:        Received unexpected error:
                        no such file or directory
          Test:         TestGetVolumeStatCapabilitiesWithoutVmMode
Log: /home/antonkuchin/src/nbs/cloud/blockstore/tools/csi_driver/internal/driver/tests/test-results/tests/testing_out_stuff/tests.TestGetVolumeStatCapabilitiesWithoutVmMode.log
Logsdir: /home/antonkuchin/src/nbs/cloud/blockstore/tools/csi_driver/internal/driver/tests/test-results/tests/testing_out_stuff
------ FAIL: 1 - FAIL cloud/blockstore/tools/csi_driver/internal/driver/tests

Total 1 suite:
  1 - FAIL
Total 1 test:
  1 - FAIL
Failed

It fails because volume is neither staged nor published in this test, so unix.Statfs(req.VolumePath, &stat) return an error. I think we have to publish volume first because spec for NodeGetVolumeStats reqires

// It can be any valid path where volume was previously
// staged or published.
...
string volume_path = 2;

In suite it passes because previous tests create and don't cleanup pod mount directory .../r3tmp/pods/test-pod-id-13/volumes/test-disk-id-42/mount.