test: physical: Fix readability-identifier-naming

```
/home/andrew/src/openbmc/phosphor-led-sysfs/build/../test/physical.cpp:15:10: error: invalid case style for function 'create_sandbox' [readability-identifier-naming,-warnings-as-errors]
fs::path create_sandbox()
         ^~~~~~~~~~~~~~
         createSandbox
```

Change-Id: I21a46563c5d75e27eff3ab1ffcc25e96025157e8
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
1 file changed