fix: only apply bg-brand-primary to SearchHeader if variant=inverse

[adamstankiewicz]

Description

Fixes the issue where there is incorrectly a background color on the SearchHeader component used across 3 MFEs.

Screenshots

Before (Bulk Enrollment)

After (Bulk Enrollment)

More details

• Dynamic theming was just recently-ish added to admin portal, so the bg-brand-primary class that was already on the SearchHeader component began to apply a style change once that class name had meaning within the admin portal MFE.
• It does not affect explore catalog because that MFE does need to support dynamic theming, so the class name there has no styles associated with it.
• In the learner portal, we use the inverse variant and actually do want the background to be the enterprise's theme color. To keep support for learner portal, but fix for the other MFEs, the bg-brand-primary class will only be applied when variant="inverse", which is only true for the learner portal.

Merge checklist:

• Evaluate how your changes will impact existing consumers (e.g., frontend-app-learner-portal-enterprise, frontend-app-admin-portal, and frontend-app-enterprise-public-catalog). Will consumers safely be able to upgrade to this change without any breaking changes?
• Ensure your commit message follows the semantic-release conventional commit message format. If your changes include a breaking change, ensure your commit message is explicitly marked as a BREAKING CHANGE so the NPM package is released as such.
• Once CI is passing, verify the package versions that Lerna will increment to in the Github Action CI workflow logs.
  • Note: This may be found in the "Preview Updated Versions (dry run)" step in the Github Action CI workflow logs.

Post merge:

• Verify Lerna created a release commit (e.g., chore(release): publish) that incremented versions in relevant package.json and CHANGELOG files, and created Git tags for those versions.
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[codecov]

Codecov Report

Merging #281 (10fa83a) into master (4776949) will increase coverage by 0.03%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #281      +/-   ##
==========================================
+ Coverage   77.46%   77.50%   +0.03%     
==========================================
  Files          34       34              
  Lines         648      649       +1     
  Branches      162      162              
==========================================
+ Hits          502      503       +1     
  Misses        133      133              
  Partials       13       13              

Impacted Files	Coverage Δ
packages/catalog-search/src/SearchHeader.jsx	92.30% <100.00%> (+0.64%)	⬆️

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