fix: fixed dynamic learner profile issue

[sundasnoreen12]

INF-385

Description

Fixed dynamic image issue by displaying dummy avatar to make it consistent throughout the discussion MFE.

How Has This Been Tested? Please describe in detail how you tested your changes.

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 coverage has no change and project coverage change: -0.02 :warning:

Comparison is base (5cc5156) 92.17% compared to head (7cedfe1) 92.15%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #493 +/- ## ========================================== - Coverage 92.17% 92.15% -0.02% ========================================== Files 163 163 Lines 3259 3251 -8 Branches 889 889 ========================================== - Hits 3004 2996 -8 Misses 236 236 Partials 19 19 ``` | [Impacted Files](https://codecov.io/gh/openedx/frontend-app-discussions/pull/493?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openedx) | Coverage Δ | | |---|---|---| | [src/discussions/learners/data/selectors.js](https://codecov.io/gh/openedx/frontend-app-discussions/pull/493?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openedx#diff-c3JjL2Rpc2N1c3Npb25zL2xlYXJuZXJzL2RhdGEvc2VsZWN0b3JzLmpz) | `100.00% <ø> (ø)` | | | [src/discussions/learners/learner/LearnerAvatar.jsx](https://codecov.io/gh/openedx/frontend-app-discussions/pull/493?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openedx#diff-c3JjL2Rpc2N1c3Npb25zL2xlYXJuZXJzL2xlYXJuZXIvTGVhcm5lckF2YXRhci5qc3g=) | `100.00% <ø> (ø)` | | | [...s/post-comments/comments/comment/CommentHeader.jsx](https://codecov.io/gh/openedx/frontend-app-discussions/pull/493?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openedx#diff-c3JjL2Rpc2N1c3Npb25zL3Bvc3QtY29tbWVudHMvY29tbWVudHMvY29tbWVudC9Db21tZW50SGVhZGVyLmpzeA==) | `100.00% <ø> (ø)` | | | [...scussions/post-comments/comments/comment/Reply.jsx](https://codecov.io/gh/openedx/frontend-app-discussions/pull/493?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openedx#diff-c3JjL2Rpc2N1c3Npb25zL3Bvc3QtY29tbWVudHMvY29tbWVudHMvY29tbWVudC9SZXBseS5qc3g=) | `58.82% <ø> (-1.18%)` | :arrow_down: | | [src/discussions/posts/data/selectors.js](https://codecov.io/gh/openedx/frontend-app-discussions/pull/493?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openedx#diff-c3JjL2Rpc2N1c3Npb25zL3Bvc3RzL2RhdGEvc2VsZWN0b3JzLmpz) | `93.75% <ø> (-0.70%)` | :arrow_down: | | [src/discussions/posts/post/PostHeader.jsx](https://codecov.io/gh/openedx/frontend-app-discussions/pull/493?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openedx#diff-c3JjL2Rpc2N1c3Npb25zL3Bvc3RzL3Bvc3QvUG9zdEhlYWRlci5qc3g=) | `89.47% <ø> (-0.27%)` | :arrow_down: | 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)

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