Ignore 404 error when fetching universal login content in branding

[sergiught]

🔧 Changes

An issue with the branding resource got pointed out in #358 after our v0.38.0 release. It turns out we removed by mistake a 404 ignore when fetching the universal login template, so we're adding it back now but also ensuring we properly add tests for that tenant flag check when flattening the struct.

📚 References

🔬 Testing

We are adding additional test cases to cover this part.

📝 Checklist

• All new/changed/fixed functionality is covered by tests (or N/A)
• I have added documentation for all new/changed functionality (or N/A)

[codecov-commenter]

Codecov Report

Base: 86.69% // Head: 86.80% // Increases project coverage by +0.11% 🎉

Coverage data is based on head (c65ea26) compared to base (1150f8f).
Patch coverage: 54.16% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #359      +/-   ##
==========================================
+ Coverage   86.69%   86.80%   +0.11%     
==========================================
  Files          40       40              
  Lines        8469     8476       +7     
==========================================
+ Hits         7342     7358      +16     
+ Misses        869      858      -11     
- Partials      258      260       +2     

Impacted Files	Coverage Δ
internal/provider/resource_auth0_branding.go	83.94% <54.16%> (+4.79%)	⬆️

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