Fix BridgeableConstraint with model_convert

[blegat]

Tried fixing jump-dev/SumOfSquares.jl#444 with Claude but he got really confused.
The root cause it that the way model_convert works is a bit unclear and inconsistent.
When you call @constraint(model, ...), we first create an AbstractConstraint with build_constraint. There we don't have the model type so we cannot convert yet.
Then, in the macro code itself we call model_convert:

JuMP.jl/src/macros/@constraint.jl

Lines 188 to 206 in 44397c7

	code = if is_vectorized
	quote
	$parse_code
	# These broadcast calls need to be nested so that the operators
	# are fused. Some broadcasted errors result if you put them on
	# different lines.
	add_constraint.(
	$model,
	model_convert.($model, $build_call),
	$name_expr,
	)
	end
	else
	quote
	$parse_code
	build = model_convert($model, $build_call)
	add_constraint($model, build, $name_expr)
	end
	end

Then we pass the converted AbstractConstraint to add_constraint which then also calls model_convert:

JuMP.jl/src/constraints.jl

Line 1046 in 44397c7

con = model_convert(model, con)

It a bit redundant. I checked and both were added in github.com//pull/3385.
The advantages of doing it in add_constraint are that 1) it's easier to maintain method implementations that macro code and 2) we don't need to do a broadcast in case of the vectorization.
In PolyJuMP, we create a constraint outside the macro so we rely on the model_convert in add_constraint.
https://github.com/jump-dev/PolyJuMP.jl/blob/571a9874547ea44efe38822e073a3aecffdb127c/src/constraint.jl#L282-L288
However, we didn't call model_convert there so that's an issue.

So there are a few ways to fix the issue in SumOfSquares. In all of them, we need the fix in model_convert of BridgeableConstraint. The question is, where should model_convert be called.
We should decide who's responsibility it is to call model_convert, is it

1. the caller of add_constraint or
2. the implementation of add_constraint.

In case

1. we should probably remove the model_convert in add_constraint(::AbstractModel, ::AbstractConstraint) (we may consider it breaking but that would only be for users that weren't using the macro so unclear if it's a big deal) and in case
2. we should add model_convert in add_constraint(::GenericModel, ::BridgeableConstraint) like done in this PR and then also remove the model_convert called from the macro.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.93%. Comparing base (44397c7) to head (c4d70a7).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4183   +/-   ##
=======================================
  Coverage   99.93%   99.93%           
=======================================
  Files          42       42           
  Lines        6230     6231    +1     
=======================================
+ Hits         6226     6227    +1     
  Misses          4        4           

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[odow]

Suggested change

	@test !(NonnegativeBridge{Int} in model.bridge_types)
	@test !(NonnegativeBridge{Int} in model.bridge_types)
	return