[no-relnotes] Add initial unit test for MIG CDI spec generation

[elezar]

This adds a basic test that fails without the changes of #619

Against v1.16.0:

--- FAIL: TestNewNvmlMIGDiscoverer (0.00s)
    --- FAIL: TestNewNvmlMIGDiscoverer/#00 (0.00s)
        nvml_test.go:161:
                Error Trace:    /Users/elezar/src/container-toolkit/internal/platform-support/dgpu/nvml_test.go:161
                Error:          Target error should be in err chain:
                                expected: ""
                                in chain: "error getting placement info: error getting GPU minor: <nil>"
                                        "error getting GPU minor: <nil>"
                Test:           TestNewNvmlMIGDiscoverer/#00
FAIL