Migrate scigateway tests to testing-library

[kennethnym]

Description

This PR migrates every unit tests scigateway to testing-library. I also improved some of the existing tests as well.

Testing instructions

Add a set up instructions describing how the reviewer should test the code

• Review code
• Check Actions build
• Review changes to test coverage

Agile board tracking

connect to #1265

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.24 🎉

Comparison is base (7ac0f60) 96.76% compared to head (e2ce0b8) 97.01%.

❗ Current head e2ce0b8 differs from pull request most recent head 0a86e5c. Consider uploading reports for the commit 0a86e5c to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1273      +/-   ##
===========================================
+ Coverage    96.76%   97.01%   +0.24%     
===========================================
  Files           43       43              
  Lines         1609     1609              
  Branches       437      437              
===========================================
+ Hits          1557     1561       +4     
+ Misses          48       45       -3     
+ Partials         4        3       -1     

Impacted Files	Coverage Δ
src/App.tsx	87.09% <ø> (+6.45%)	⬆️
src/loginPage/loginPage.component.tsx	96.45% <ø> (-2.13%)	⬇️
src/notifications/notificationBadge.component.tsx	100.00% <ø> (ø)
src/accessibilityPage/contactUs.component.tsx	100.00% <100.00%> (ø)

... and 7 files with indirect coverage changes

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[louise-davies]

Overall looks good other than my minor comment. I added a couple of commits to 1) remove the spam from the test console I found when I ran the tests locally and 2) to recreate the test you skipped in App.test.tsx. Let me know your thoughts on my changes :)