Fix panic in cleanupInvalidVolumeMounts

[MissiontoMars]

Why are these changes needed?

Removing elements while iterating over VolumeMounts slice causes panics.

WARN[0000] ingress class annotation is not set for cluster default/raycluster-sample 
--- FAIL: TestCleanupInvalidVolumeMounts (0.00s)
panic: runtime error: index out of range [2] with length 2 [recovered]
        panic: runtime error: index out of range [2] with length 2

goroutine 103 [running]:
testing.tRunner.func1.2({0x10543be80, 0x14000042468})
        /usr/local/go/src/testing/testing.go:1389 +0x1c8
testing.tRunner.func1()
        /usr/local/go/src/testing/testing.go:1392 +0x384
panic({0x10543be80, 0x14000042468})
        /usr/local/go/src/runtime/panic.go:838 +0x204
github.com/ray-project/kuberay/ray-operator/controllers/ray/common.cleanupInvalidVolumeMounts(...)
        /Users/wanxing/work/code/kuberay-github/ray-operator/controllers/ray/common/pod.go:789
github.com/ray-project/kuberay/ray-operator/controllers/ray/common.TestCleanupInvalidVolumeMounts(0x1400020b520?)
        /Users/wanxing/work/code/kuberay-github/ray-operator/controllers/ray/common/pod_test.go:636 +0x500
testing.tRunner(0x1400020b6c0, 0x1054f51c0)
        /usr/local/go/src/testing/testing.go:1439 +0x110
created by testing.(*T).Run
        /usr/local/go/src/testing/testing.go:1486 +0x300
exit status 2

Related issue number

Checks

• I've made sure the tests are passing.
• Testing Strategy
  • Unit tests
  • Manual tests
  • This PR is not tested :(

[MissiontoMars]

@Jeffwan @Basasuya

[Jeffwan]

Nice catch. I think the slice manipulation is not that elegant in this case. The fix looks good to me.