Draft: delete useless bold when user select mask variable in ci/cd variables modale

What does this MR do and why?

When I toggle the masked variable setting in "add variable" form the help text is no more bold. As described in #364856 (closed)

Screenshots or screen recordings

How to set up and validate locally

Go to Settings > CI/CD > Variables, click to "Add variable" and toggle the "Mask variable" option on and off.

MR acceptance checklist

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Related to #364856 (closed)