fix: multi workers devtools source loading

[edmundhung]

Fixes #11769

Describe your change...

---

• Tests
  • Tests included/updated
  • Automated tests not possible - manual testing has been completed as follows:
  • Additional testing not necessary because:
• Public documentation
  • Cloudflare docs PR(s):
  • Documentation not necessary because:

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Latest commit: 3a446d8

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commit: 3a446d8