Add CSS fixes for issuables drawer

What does this MR do and why?

1. This MR fixes an error Injection "isGroup" is not found when issuables drawer is open
2. Removes an unnecessary top padding in the drawer
3. Changes line-height to inherit so that line spacing is consistent between standalone work item and a drawer

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Enable issuable drawer feature flag:

   Feature.enable(:issuesListDrawer)

2. Visit any project
3. Click on any issue in the project issues list

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #419518