We have a ui test to ensure we emit an error if we encounter too big
enums. Before this fix, compiling the test with `-Cdebuginfo=2` would
not include the span of the instantiation site, because the error is
then emitted from a different code path that does not include the span.
Propagate the span to the error also in the debuginfo case, so the test
passes regardless of debuginfo level.
To reduce risk of regressing on generating debuginfo e.g. in the form of
ICE:s. This will also ensure that future ui tests support different
debuginfo levels.
When I looked at run time for different CI jobs, **x86_64-gnu-debug**
was far from the bottle neck, so it should be fine to make it perform
more work.
