Stage pr created to slack stage

[mokimo]

• Pass the environment variable to the correct workflow Correctly send the created PR slacks #2566
• Remove files from not-merged PRs from the seen map. This lead to Mwpw-142267: Merch What's Included and Merch Mnemonic List (TwP) #2554 (comment) not being merged despite no file collisions.

Resolves: MWPW-152624

Test URLs:

• Before: https://main--milo--adobecom.aem.live/?martech=off
• After: https://stage-pr-created-to-slack-stage--milo--mokimo.aem.live/?martech=off

[aem-code-sync]

Page	Scores	Audits	Google
/?martech=off

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.86%. Comparing base (d932b35) to head (dcc0800).

Additional details and impacted files

@@            Coverage Diff             @@
##            stage    #2572      +/-   ##
==========================================
+ Coverage   95.84%   95.86%   +0.01%     
==========================================
  Files         176      176              
  Lines       46149    46149              
==========================================
+ Hits        44230    44239       +9     
+ Misses       1919     1910       -9     

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[github-actions]

Reminder to set the Ready for Stage label - to queue this to get merged to stage & production.