Fix naming of header and variable in NDPluginAttribute tests

[jwlodek]

Naming was changed in previous PR, and the PR with these tests was merged before the changed names were applied

[ericonr]

  /home/runner/work/ADCore/ADCore/ADApp/pluginTests/O.linux-x86_64/../test_NDPluginAttribute.cpp:71:(.text+0xa37): undefined reference to `compressZlib(NDArray*, int, NDCodecStatus_t*, char*)'
  /usr/bin/ld: /home/runner/work/ADCore/ADCore/ADApp/pluginTests/O.linux-x86_64/../test_NDPluginAttribute.cpp:71:(.text+0x2717): undefined reference to `compressZlib(NDArray*, int, NDCodecStatus_t*, char*)'
  collect2: error: ld returned 1 exit status

[ericonr]

Can you wrap the text of the second commit? Something like

Expose NDPluginCodec functions with NDPLUGIN_API

This way, the compress/decompress functions can be accessed with
-fvisibility=hidden.

This fixes linking test_NDPluginAttribute with function compressZlib.

[jwlodek]

Done