Fix slack integration for e2e tests

[luhi-DT]

Description

Currently the e2e tests are not reporting the status in slack, as the interface changed with https://github.com/Dynatrace/dynatrace-operator/pull/4060/files

How can this be tested?

Run e2e test action and check if slack notifications are coming in

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 64.68%. Comparing base (e7f1de9) to head (938a989).
Report is 1 commits behind head on main.

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4085   +/-   ##
=======================================
  Coverage   64.68%   64.68%           
=======================================
  Files         397      397           
  Lines       26509    26509           
=======================================
  Hits        17148    17148           
  Misses       8031     8031           
  Partials     1330     1330           

Flag	Coverage Δ
unittests	64.68% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

---

🚨 Try these New Features:

• Flaky Tests Detection - Detect and resolve failed and flaky tests