Refactor: pass backend explicitly when creating pipeline engine runtime

[6543]

smal refactor taken from #6166

[woodpecker-bot]

Surge PR preview deployment was removed

[codecov]

Codecov Report

❌ Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 32.43%. Comparing base (9f9aa72) to head (65eeccc).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
agent/runner.go	0.00%	2 Missing ⚠️
pipeline/runtime/runtime.go	0.00%	2 Missing ⚠️
cli/exec/exec.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6268      +/-   ##
==========================================
+ Coverage   32.41%   32.43%   +0.02%     
==========================================
  Files         420      420              
  Lines       28318    28314       -4     
==========================================
+ Hits         9180     9185       +5     
+ Misses      18289    18280       -9     
  Partials      849      849              

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