Bump k6-browser Go module version to 1.20

[inancgumus]

What?

Bumps the Go module version to 1.20.

Why?

The browser team wants to use the new multi-error feature.

Checklist

• I have performed a self-review of my code.
• I have added tests for my changes.
• I have run linter locally (make lint) and all checks pass.
• I have run tests locally (make tests) and all tests pass.
• I have commented on my code, particularly in hard-to-understand areas.

Related PR(s)/Issue(s)

N/A

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (32c5f12) 73.07% compared to head (0d16c43) 73.54%.
Report is 2 commits behind head on master.

❗ Current head 0d16c43 differs from pull request most recent head 800fb1a. Consider uploading reports for the commit 800fb1a to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3590      +/-   ##
==========================================
+ Coverage   73.07%   73.54%   +0.46%     
==========================================
  Files         281      277       -4     
  Lines       21102    20200     -902     
==========================================
- Hits        15421    14856     -565     
+ Misses       4705     4397     -308     
+ Partials      976      947      -29     

Flag	Coverage Δ
macos	73.44% <100.00%> (+0.43%)	⬆️
ubuntu	73.46% <100.00%> (+0.45%)	⬆️
windows	73.38% <100.00%> (+0.43%)	⬆️

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