Fix color of the GlLabel according to Figma

What does this MR do?

On the Figma color $gray-950(#1f1f1f) used for labels but currently using #333333 color, according to 4:5:1 ratio when color needs to be dark.

Also, on the right side of the scoped label, color is currently changing based on the label color, but on the Figma it is always $gray-950(#1f1f1f).

I have fixed these things.

Current	This MR

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines.
• GitLab UI's contributing guidlines.
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• Added the ~"component:*" label(s) if applicable.

Security

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Accessibility

If this MR adds or modifies a component, take a few moments to review the following:

• All actions and functionality can be done with a keyboard.
• Links, buttons, and controls have a visible focus state.
• All content is presented in text or with a text equivalent. For example, alt text for SVG, or aria-label for icons that have meaning or perform actions.
• Changes in a component’s state are announced by a screen reader. For example, changing aria-expanded="false" to aria-expanded="true" when an accordion is expanded.
• Color combinations have sufficient contrast.

Closes #1503 (closed)