Fixes update seats with wrong body: expected array, sent single object

[auyer]

Description

The expected body is an array. Thus I fixes the body in the existing method, and added a method for multiple UserSeeats.
I can also remove the new method, and make the existing one take a list.
83c7769 fixes #1479

Has your change been tested?

Yes. I made requests using this, and wrote tests to cover it.

Types of changes

What sort of change does your code introduce/modify?

• 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:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• [?] I have updated the documentation accordingly. (not sure if I should add docs elsewhere)
• I have added tests to cover my changes.
• All new and existing tests passed.
• This change is using publicly documented in cloudflare/api-schemas
  and relies on stable APIs.

[github-actions]

changelog detected ✅

[codecov-commenter]

Codecov Report

Attention: 544 lines in your changes are missing coverage. Please review.

Comparison is base (b9ac804) 48.33% compared to head (4941c2c) 53.61%.
Report is 591 commits behind head on master.

Files	Patch %	Lines
api_shield_schemas.go	54.81%	35 Missing and 26 partials ⚠️
observatory.go	54.68%	29 Missing and 29 partials ⚠️
per_hostname_tls_settings.go	41.86%	25 Missing and 25 partials ⚠️
dlp_dataset.go	45.45%	24 Missing and 24 partials ⚠️
logpush.go	48.86%	43 Missing and 2 partials ⚠️
devices_policy.go	56.96%	23 Missing and 11 partials ⚠️
access_users.go	76.84%	11 Missing and 11 partials ⚠️
d1.go	70.27%	11 Missing and 11 partials ⚠️
access_custom_page.go	58.33%	10 Missing and 10 partials ⚠️
page_shield_policies.go	60.86%	9 Missing and 9 partials ⚠️
... and 19 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1480      +/-   ##
==========================================
+ Coverage   48.33%   53.61%   +5.27%     
==========================================
  Files         133      156      +23     
  Lines       13023    11922    -1101     
==========================================
+ Hits         6295     6392      +97     
+ Misses       5201     3675    -1526     
- Partials     1527     1855     +328     

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[github-actions]

This functionality has been released in v0.87.0.

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