[MM-350] Fix issue in create issue modal and attach issue modal

[ayusht2810]

Summary

• Fixed issue of repository list not updating when there was incorrect ogranisation in the system console setting for Create GitHub Issue modal
• Fixed issue of getting error of unexpected json when opening Attach to GitHub Issue modal for the above-mentioned case

Ticket Link

Fixes #557

Checklist

• [x] Completed dev testing
• [x] make test Ran test cases and ensured they are passing
• [x] make check-style Ran style check and ensured both webapp and server pass the checks

What to test?

• Check the dropdown values for repository present in the Create GitHub Issue modal
• Check the dropdown values for github issue present in the Attach to GitHub Issue modal

How to test?

• Add GitHub Organisation in the system console settings
• Check the dropdowns mentioned above
• Update the GitHub Organisation again in the system console settings by adding some incorrect value
• Check the dropdown values again

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 16.15%. Comparing base (da4c4df) to head (40626e3). Report is 8 commits behind head on master.

:exclamation: Current head 40626e3 differs from pull request most recent head 1b57a12

Please upload reports for the commit 1b57a12 to get more accurate results.

Files	Patch %	Lines
server/plugin/api.go	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #761 +/- ## ========================================== - Coverage 16.16% 16.15% -0.01% ========================================== Files 17 17 Lines 6021 6022 +1 ========================================== Hits 973 973 - Misses 5003 5004 +1 Partials 45 45 ```

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[mickmister]

@wiggin77 This is ready for merge :+1: