ci: avoid hitting MAX_PATHLEN in win32 builds

[DonIsaac]

What does this PR do?

Branches with long names can be just enough to put paths to cached webkit header/object files past windows' max path length of 4096 260. Discovered in #16294. Example here

[robobun]

^{Updated 5:16 PM PT - Jan 9th, 2025}

✅ @DonIsaac, your commit a069d63 has passed in #9334! 🎉

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🧪   try this PR locally:

bunx bun-pr 16299

[Jarred-Sumner]

where is 4096 as the max path length coming from?

[DonIsaac]

My mistake, it's actually 260.