IntSet tests in release-0.18 branch are broken on julia 1.9+

[oxinabox]

Works fine in 1.8 but but after 1.9 it fails.
Master branch has it working fine.
I haven't looked into why

[StephenVavasis]

I have traced the problem to a bug in Base.map!. I have opened an issue:
JuliaLang/julia#50780

[StephenVavasis]

Sorry, I got this wrong: map!(|,a,b) does not replace a with the bitwise OR of a and b as I had assumed, as explained by the respondent to my issue JuliaLang/julia#50780 . However, I now don't understand how union of IntSets ever worked. Line 94 of int_set.jl seems to rely on the fact that map!(|,a,b) replaces a with a bitwise OR. I will try to return to this later.

[StephenVavasis]

OK, I figured it out: the bug is in Base.map!(|,a,a,b) not Base.map!(|,a,b) as I said earlier. I reopened my issue.

[laborg]

The underlying issue has been fixed. This issue can be closed.