This test verifies that we can export constants with unknown kind.
Previously, the exporter would panic while attempting to convert such constants
to their target type (float64, in this case).
-- flags --
-min_go=go1.20
-- go.mod --
module mod.txt/p
go 1.20
-- p.go --
package p
const EPSILON float64 = 1e- //@diag(re"1e-()", re"exponent has no digits")