state: Fix TestReadEPsFromDirNames unit test
state: Fix TestReadEPsFromDirNames unit test

The unit test started failing in the development vagrant box:
```
state_test.go:187:
    c.Assert(len(eps), Equals, len(epsWanted))
... obtained int = 0
... expected int = 4
```

The offending error was:
```
level=warning msg="Regeneration of endpoint failed" bpfCompilation=0s buildDuration=1.133726ms containerID= datapathPolicyRevision=0 desiredPolicyRevision=1 endpointID=259 error="error synchronizing endpoint BPF program directories: unable to rename current endpoint directory: rename /tmp/cilium-tests682674000/259 259_stale: permission denied" ipv4= ipv6= k8sPodName=/ mapSync=0s policyCalculation=0s prepareBuild="348.77µs" proxyConfiguration=0s proxyPolicyCalculation=0s proxyWaitForAck=0s reason=test subsys=endpoint waitingForCTClean=0s waitingForLock="4.134µs"
```

The cause of this was that although state_test.go would create a temporary
state directory. It would fail to os.Chdir() which caused directory operations
to be performed in the real state directory which would then fail because of
permissions.

Fixes: #5716

Signed-off-by: Thomas Graf <5f50a84c1fa3bcff146405017f36aec1a10a9e38@cilium.io>

tgraf/cilium,michi-covalent/cilium,scanf/cilium,cilium-team/cilium,tklauser/cilium,cilium/cilium,cilium/cilium,scanf/cilium,tgraf/cilium,tklauser/cilium,tgraf/cilium,tgraf/cilium,michi-covalent/cilium,tgraf/cilium,scanf/cilium,michi-covalent/cilium,scanf/cilium,tklauser/cilium,cilium-team/cilium,michi-covalent/cilium,cilium/cilium,scanf/cilium,tgraf/cilium,tklauser/cilium,scanf/cilium,michi-covalent/cilium,cilium/cilium,cilium/cilium,tklauser/cilium,scanf/cilium