Ran into this same issue
Had to update the runner to macos-13
macos-latest defaults to version 12 which does not support xcode 15
emd
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I ran into this same issue, the problem was with github actions.
We had our runner set to macos-latest. This uses macos version 12 which does not support xcode version 15.
Had to update the runs-on to macos-13 and in our Fastfile we specify the version of code to 15.2.