Mark job posting template as experimental

[kmike]

It is useful as-is, but there are known issues - e.g. JS pagination is common on job websites, and it's not handled by the spider, so on many websites it can only extract jobs from the first page.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.35%. Comparing base (78c495c) to head (3367b0d).
Report is 2 commits behind head on job-posting-product-list.

Additional details and impacted files

@@                    Coverage Diff                    @@
##           job-posting-product-list     #102   +/-   ##
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  Coverage                     95.35%   95.35%           
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  Files                            26       26           
  Lines                          2604     2604           
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  Hits                           2483     2483           
  Misses                          121      121           

Files with missing lines	Coverage Δ
zyte_spider_templates/spiders/job_posting.py	95.69% <ø> (ø)