fix: action dropdown UI issues

[sundasnoreen12]

INF-848

Description

Response sort modal popup is displayed above the actions dropdown menu because the z-index is same for both.

AC:

1. Actions Dropdown should be above response sort menu
2. Check if actions dropdown menu is above the header (for mobile view)
3. Make sure response sort popup is also responding in correct order (for mobile view)

Screenshots:

Before	After

Merge Checklist

• [ ] If your update includes visual changes, have they been reviewed by a designer? Send them a link to the Sandbox, if applicable.
• [ ] Is there adequate test coverage for your changes?

Post-merge Checklist

• [ ] Deploy the changes to prod after verifying on stage or ask @openedx/edx-infinity to do it.
• [ ] 🎉 🙌 Celebrate! Thanks for your contribution.

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (f1a9922) 92.17% compared to head (e8e1d10) 92.17%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #500 +/- ## ======================================= Coverage 92.17% 92.17% ======================================= Files 164 164 Lines 3259 3259 Branches 891 891 ======================================= Hits 3004 3004 Misses 236 236 Partials 19 19 ``` Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openedx). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openedx)

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Do you have feedback about the report comment? Let us know in this issue.