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>
diff --git a/test/physical.cpp b/test/physical.cpp
index adf5d06..5058049 100644
--- a/test/physical.cpp
+++ b/test/physical.cpp
@@ -12,7 +12,7 @@
 using Action = sdbusplus::xyz::openbmc_project::Led::server::Physical::Action;
 namespace fs = std::filesystem;
 
-fs::path create_sandbox()
+fs::path createSandbox()
 {
     /* If your tests need to touch the filesystem, always use mkdtemp() or
      * mkstemp() for creating directories and files. Tests can be run in
@@ -45,7 +45,7 @@
 {
   public:
     /* Use a no-args ctor here to avoid headaches with {Nice,Strict}Mock */
-    MockLed() : SysfsLed(create_sandbox())
+    MockLed() : SysfsLed(createSandbox())
     {}
 
     virtual ~MockLed()