Handle `buildaction "Copy"` for gmake2.

[Jarod42]

What does this PR do?

Handle buildaction "Copy" for gmake2.

How does this PR change Premake's behavior?

Handle buildaction "Copy" for gmake2.

Anything else we should know?

Tested with https://github.com/Jarod42/premake-sample-projects/tree/master/projects/project-buildaction_copy https://github.com/Jarod42/premake-sample-projects/actions/runs/7961205332/job/21731877841

Did you check all the boxes?

• [x] Focus on a single fix or feature; remove any unrelated formatting or code changes
• [x] Add unit tests showing fix or feature works; all tests pass
• [ ] Mention any related issues (put closes #XXXX in comment to auto-close issue when PR is merged)
• [x] Follow our coding conventions
• [x] Minimize the number of commits
• [ ] Align documentation to your changes

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