Fix broadcasting f-in-set in constraint macro

[odow]

x-ref #3629

So this line was never covered:
https://app.codecov.io/gh/jump-dev/JuMP.jl/commit/419c3344c9a62692e344da745765ac7daec95c01/blob/src/macros.jl#L839

The Ref was added here:
https://github.com/jump-dev/JuMP.jl/pull/1438/files#diff-e628f2d30670b1af0cdd9c9c520aaddc44021cd503e169d767ec49c95f189264R288

I guess because we didn't yet have:
jump-dev/MathOptInterface.jl@ed08ee9

I think it's because only the .∈ syntax supports this. You can't . the in-fix in operator:

julia> dump(:(x .in y))
ERROR: syntax: space before "." not allowed in "x ." at REPL[76]:1
Stacktrace:
 [1] top-level scope
   @ none:1

julia> dump(:(x in. y))
ERROR: syntax: invalid identifier name "."
Stacktrace:
 [1] top-level scope
   @ none:1

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2896184) 98.22% compared to head (d6fc941) 98.24%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3632      +/-   ##
==========================================
+ Coverage   98.22%   98.24%   +0.01%     
==========================================
  Files          43       43              
  Lines        5636     5636              
==========================================
+ Hits         5536     5537       +1     
+ Misses        100       99       -1     

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