Don't always run php for DPP_CORO

[supsm]

If DPP_CORO is configured to be true, the make_struct.php will always be run, even if not on UNIX or if PHP isn't found. This PR moves the relevant execute_process to where the other php files are run.

Code change checklist

• I have ensured that all methods and functions are fully documented using doxygen style comments.
• My code follows the coding style guide.
• I tested that my change works before raising the PR.
• I have ensured that I did not break any existing API calls.
• I have not built my pull request using AI, a static analysis tool or similar without any human oversight.

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[github-actions]

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[supsm]

oops