Fix printing when show called on invalid variable or constraint

[odow]

Closes https://github.com/jump-dev/JuMP.jl/issues/3762

• [x] Test extensions: https://github.com/jump-dev/JuMP.jl/actions/runs/9312266581

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 98.38%. Comparing base (99ab0b2) to head (78018cc).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #3763 +/- ## ======================================= Coverage 98.38% 98.38% ======================================= Files 44 44 Lines 5873 5879 +6 ======================================= + Hits 5778 5784 +6 Misses 95 95 ```

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[odow]

So you're okay with just printing "InvalidXXX"?

[blegat]

Yes, the variable is invalid so using it in a model should throw but we could allow printing it and InvalidXXX seems reasonable.