Make it build cleanly on GHC 8.10.7 and GHC 9.4.7
This MR makes this project build cleanly on both GHC 8.10.7 and GHC 9.4.7
As stated in another MR the removal of panic
is justified by the forward-compatibility story (not to mention that recent versions of error
attaches a CallStack
by default, so there is no advantage in using panic
in the first place).