test(bigtable): Convert entry error to status

[bhshkh]

b/387315971
Fixes TestMutateRows_NoRetry_NonTransientErrors conformance test

=== RUN   TestMutateRows_NoRetry_NonTransientErrors
    mutaterows_test.go:184: 
        	Error Trace:	/usr/local/google/home/bahaaiman/Documents/cfdb-workspace-01/cloud-bigtable-clients-test/tests/mutaterows_test.go:184
        	Error:      	Not equal: 
        	            	expected: 7
        	            	actual  : 0
        	Test:       	TestMutateRows_NoRetry_NonTransientErrors
    mutaterows_test.go:184: 
        	Error Trace:	/usr/local/google/home/bahaaiman/Documents/cfdb-workspace-01/cloud-bigtable-clients-test/tests/mutaterows_test.go:184
        	Error:      	Not equal: 
        	            	expected: 7
        	            	actual  : 0
        	Test:       	TestMutateRows_NoRetry_NonTransientErrors
--- FAIL: TestMutateRows_NoRetry_NonTransientErrors 

In this test, the response returned by the library'y ApplyBulk method is

errs: [<nil>,  rpc error: code = PermissionDenied desc = , rpc error: code = PermissionDenied desc = , <nil>]
err: <nil>

Each of the errors in the errs variable should be converted to status to match the format expected by the test proto. This change is being in this PR.

After fix:

=== RUN   TestMutateRows_NoRetry_NonTransientErrors
--- PASS: TestMutateRows_NoRetry_NonTransientErrors (0.01s)
PASS
ok  	github.com/googleapis/cloud-bigtable-clients-test/tests	0.026s