fix: stacks listed twice

[i4ki]

The root cause was stacks listed twice and the incorrect one was missing the changed flag, so the run-order put them in a map, randomly overwriting the entry, so in the end stacks could have a changed flag or not, so the run-order was broken.

It's a bit hard to reproduce because it only happens when a stack detected as changed also had a module that changed, so I'm going to provide a testcase later this week.

[codecov-commenter]

Codecov Report

Merging #149 (d5acd04) into main (92d3679) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #149      +/-   ##
==========================================
- Coverage   60.72%   60.69%   -0.03%     
==========================================
  Files          29       29              
  Lines        4524     4526       +2     
==========================================
  Hits         2747     2747              
- Misses       1629     1631       +2     
  Partials      148      148              

Flag	Coverage Δ
tests	60.69% <100.00%> (-0.03%)	⬇️

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

Impacted Files	Coverage Δ
manager.go	67.57% <100.00%> (+0.50%)	⬆️
stack/loader.go	50.94% <0.00%> (-1.42%)	⬇️

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[katcipis]

Thanks for the quick fix 🚀