chore(tests): Cleanup bootstrap.php to be forward-compatible

[come-nc]

This uses the new tests/autoload.php from nextcloud/server instead of messing directly with OC private autoloader.

See nextcloud/server#52951 and nextcloud/server#52945 for context.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 65.62%. Comparing base (3ead8eb) to head (8b60d81).
Report is 2 commits behind head on main.

Additional details and impacted files

@@              Coverage Diff              @@
##               main    #4475       +/-   ##
=============================================
+ Coverage     11.03%   65.62%   +54.58%     
  Complexity      265      265               
=============================================
  Files           122       26       -96     
  Lines          5589      771     -4818     
  Branches       1209        0     -1209     
=============================================
- Hits            617      506      -111     
+ Misses         4850      265     -4585     
+ Partials        122        0      -122     

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[welcome]

Thanks for your first pull request and welcome to the community! Feel free to keep them coming! If you are looking for issues to tackle then have a look at this selection: https://github.com/nextcloud/contacts/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22