cli exec: have uniq prefix for each workflow

[6543]

preparation to have cli exec run workflows in parallel

fix taken from #6490 (6c88ea3)

[woodpecker-bot]

Surge PR preview deployment was removed

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 44.79%. Comparing base (31dd64f) to head (ca5ea22).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6716      +/-   ##
==========================================
+ Coverage   44.75%   44.79%   +0.04%     
==========================================
  Files         436      436              
  Lines       29190    29189       -1     
==========================================
+ Hits        13063    13075      +12     
+ Misses      15023    15011      -12     
+ Partials     1104     1103       -1     

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[qwerty287]

How does removing the prefix make it unique? I scanned through the compiler code but couldn't find a place where it's generated if not set

[6543]

woodpecker/pipeline/frontend/builder/builder.go

Line 221 in 31dd64f

compiler.WithPrefix(

it was just overloaded here ...