Using the expected variable to set the custom select height

[straube]

In the current v4-dev branch, the variable $custom-select-height is not being used in the _custom-forms.scss file. Instead, its default value is set there: $input-height. So, when one tries to change that variable's value it doesn't lead to the expected result. To fix that I'm simply using the variable from _variables.scss to set the .custom-select height.

[straube]

After the last time I updated this pull request branch the build failed. The output shows an error that doesn't seem to be related to the code. I'm wondering if re-building it would make the checks to pass. Is that even possible?

[mdo]

@straube It was unrelated I imagine—Travis had some issues after patching those major vulnerabilities.

[unrevised6419]

As $custom-select-height is $input-height int _variables.scss. This will fix height for sure.
#25331