add coverage for `<<error-type>>` + Sendable diagnostic issue
add coverage for `<<error-type>>` + Sendable diagnostic issue

when a variable with type `<<error-type>>` was captured in a
sendable function's environment, we use to emit a diagnostic
about it not being sendable, but it's for a bogus type.

at some point this issue disappeared as the sendable implementation
evolved, but this commit adds regression coverage.

resolves rdar://82452688

apple/swift,rudkx/swift,atrick/swift,apple/swift,benlangmuir/swift,glessard/swift,apple/swift,JGiola/swift,glessard/swift,glessard/swift,glessard/swift,roambotics/swift,ahoppen/swift,roambotics/swift,benlangmuir/swift,apple/swift,ahoppen/swift,glessard/swift,atrick/swift,rudkx/swift,benlangmuir/swift,benlangmuir/swift,gregomni/swift,glessard/swift,rudkx/swift,roambotics/swift,JGiola/swift,roambotics/swift,atrick/swift,gregomni/swift,rudkx/swift,JGiola/swift,benlangmuir/swift,atrick/swift,JGiola/swift,gregomni/swift,rudkx/swift,gregomni/swift,ahoppen/swift,benlangmuir/swift,gregomni/swift,gregomni/swift,ahoppen/swift,roambotics/swift,JGiola/swift,apple/swift,roambotics/swift,JGiola/swift,atrick/swift,ahoppen/swift,rudkx/swift,apple/swift,atrick/swift,ahoppen/swift