Change playwright tests to not run in parallell

[ghost]

Description

Related Issue(s)

• #{issue number}

Verification

• Your code builds clean without any errors or warnings
• Manual testing done (required)
• Relevant automated test added (if you find this hard, leave it and we'll help out)

Documentation

• User documentation is updated with a separate linked PR in altinn-studio-docs. (if applicable)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (b03ba7b) 87.90% compared to head (42de52a) 87.89%.
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12216      +/-   ##
==========================================
- Coverage   87.90%   87.89%   -0.01%     
==========================================
  Files         970      970              
  Lines       13813    13813              
  Branches     1704     1704              
==========================================
- Hits        12142    12141       -1     
- Misses       1461     1462       +1     
  Partials      210      210              

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