Fallback on background callback function names if source cannot be found

[corebit-nl]

Additional patch to #2922 to fully fix #1885 . Re-submitted version of #3072 .

This MR adds a patch made in #2922 to similar code, to make background callbacks fully work in compiled binaries (eg. PyInstaller).

Contributor Checklist

• [ ] I have run the tests locally and they passed. (refer to testing section in contributing)
• [ ] I have added tests, or extended existing tests, to cover any new features or bugs fixed in this PR

optionals

• [ ] I have added entry in the CHANGELOG.md
• [ ] If this PR needs a follow-up in dash docs, community thread, I have mentioned the relevant URLS as follows
  • [ ] this GitHub #PR number updates the dash docs
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