"Unexpected internal error" when trying to add a return type to a method

[AdRiley]

This change https://github.com/enso-org/enso/pull/11086/files has resulted in

Error: de_ci::program::command: sbt ℹ️ [ERROR] [2024-09-16T13:11:10.305] [org.enso.runner.Main] Unexpected internal error
INFO ide_ci::program::command: sbt ℹ️ org.graalvm.polyglot.PolyglotException: org.enso.compiler.core.CompilerError: Compiler Internal Error: Blanks should not be present during dataflow analysis.

https://github.com/enso-org/enso/actions/runs/10882555757/job/30193845599?pr=11086#step:7:1077