pipeline runtime: move setting step environment variables into own func and add CI_PIPELINE_STATUS back

[6543]

close #4337

[6543]

note: blocked till release

[woodpecker-bot]

Surge PR preview deployment was removed

[codecov]

Codecov Report

❌ Patch coverage is 73.68421% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 41.20%. Comparing base (f3e3b83) to head (ef2abcc).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
pipeline/runtime/step.go	73.68%	3 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6516      +/-   ##
==========================================
- Coverage   41.20%   41.20%   -0.01%     
==========================================
  Files         431      431              
  Lines       28850    28855       +5     
==========================================
+ Hits        11887    11889       +2     
- Misses      15893    15895       +2     
- Partials     1070     1071       +1     

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[xoxys]

Code LGTM but untested.