Improve course instance offered tests

[natalynyu]

The original tests related to updating the offered field value were not explicitly defining the original offered value, potentially causing typeorm to find retired courses and trying to unretire them. This could be what is potentially causing the tests to fail in the build. These changes explicitly define the original and updated retired values so that the original course instance selected is not one that unexpectedly has a retired value for the offered field.

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] I have run eslint on the code
• [x] I have added JSDoc for all of my code (where applicable)
• [x] I have added tests to cover my changes.

Priority:

• [ ] Normal
• [x] High

Related Issues:

Fixes #628

[codecov[bot]]

Codecov Report

Merging #669 (b293fcf) into develop (8096d72) will not change coverage. The diff coverage is 92.85%.

:exclamation: Current head b293fcf differs from pull request most recent head 07e1fe3. Consider uploading reports for the commit 07e1fe3 to get more accurate results

@@           Coverage Diff            @@
##           develop     #669   +/-   ##
========================================
  Coverage    94.19%   94.19%           
========================================
  Files          195      195           
  Lines         4602     4602           
  Branches       567      567           
========================================
  Hits          4335     4335           
  Misses         149      149           
  Partials       118      118           

Impacted Files	Coverage Δ
...lient/components/pages/utils/deduplicateCourses.ts	90.90% <90.90%> (ø)
.../components/pages/Faculty/FacultyScheduleTable.tsx	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

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