tests: Compile SWFs *before* loading them

[moulins]

Otherwise the test runner will either fail to load the SWF (if it doesn't exist yet), or load the wrong version (if the source code changed).

Checklist

• I, a human, have self-reviewed this PR and fully understand the changes within.
• [N/A] I have made or updated tests where possible.
• All of my commits are properly scoped, compile successfully, and pass all tests.
• This PR does not make sense to split up into smaller PRs.
• An LLM was involved in the authoring of this code.