Fixed error of tests failing

[matthew-kapp]

Checklist

• Appropriate tests were added | Based on existing tests
• Any code changes were done in a way that does not break public API
• All documentation related to code changes were updated | Not applicable
• The new code follows the
  contributor guidelines, in particular the SciML Style Guide and
  COLPRAC.
• Any new documentation only uses public API

Additional context

Test error fix

• Currently, when running Pkg.test(), the following error is shown:
  Testing Running tests... Unbound type parameters detected: [1] var"#__VariableResistor__#18"(name, T_dep, enforce_bounds, R_ref::Union{Missing, Nothing, ModelingToolkit.NoValue, var"##608"}, T_ref::Union{Missing, Nothing, ModelingToolkit.NoValue, var"##609"}, R_const::Union{Missing, Nothing, ModelingToolkit.NoValue, var"##610"}, pos::Union{Missing, Nothing, ModelingToolkit.NoValue, Real}, R::Union{Missing, Nothing, ModelingToolkit.NoValue, var"##611"}, alpha::Union{Missing, Nothing, ModelingToolkit.NoValue, var"##612"}, ::typeof(ModelingToolkitStandardLibrary.Electrical.__VariableResistor__)) where {var"##608", var"##609", var"##610", var"##611", var"##612"} @ ModelingToolkitStandardLibrary.Electrical none:0 Aqua: Test Failed at C:\Users\matth\.julia\packages\Aqua\epbUr\src\unbound_args.jl:37
• Now, when running Pkg.test(), the following is shown:
  Testing Running tests... Test Summary: | Pass Total Time Aqua | 10 10 3m36.8s 217.025357 seconds (37.22 M allocations: 2.340 GiB, 3.87% gc time, 10.94% compilation time: 2% of which was recompilation)
• The modification involves removing 'unit =' descriptors from the parameters and variables in VariableResistor.
• Fixes Issue QA tests fail due to Unbound Error in VariableResistor #364

Documentation build partial fix

• Fixes the error of documentation build failing. It is trying to go to a Mathworks link, which works manually, but it throws a 403 error during docs building. A linkcheck_ignore is added in docs/make.jl to ignore this specific link, and allow the docs build process to finish.
• There is a remaining error of the DC Motor + PI controller example, where the bode plot does not work. I don't know enough about the control library to fix this.

[matthew-kapp]

I see 3 tests that are passing that weren't passing before.

[AayushSabharwal]

Thanks for catching this! I noticed the QA errors but didn't notice that the incorrect units were the issue.

[matthew-kapp]

@AayushSabharwal ready for merge?