Remove inconsistent font weight for sidebar's labels

What does this MR do?

Removes the .bold css class from the sidebar label default value so that it is no longer bold 😄

None => None

Are there points in the code the reviewer needs to double check?

None

Why was this MR needed?

Fixes a UI inconsistency

What are the relevant issue numbers?

Closes #21141 (closed)

Screenshots (if relevant)

Before:

After:

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Tests
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together