Fix detach not correctly executed when changeset is in failed state

Created by: eseliger

This also fixes a second bug where imported changesets could not be detached after a failed import (eg. 404 error).

This screenshot shows that a changeset is not properly detached after it failed publishing:

Created by: codecov[bot]

Codecov Report

Merging #17526 (36a7480) into main (15afbaf) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main   #17526   +/-   ##
=======================================
  Coverage   51.70%   51.71%           
=======================================
  Files        1717     1717           
  Lines       85366    85374    +8     
  Branches     7608     7608           
=======================================
+ Hits        44142    44153   +11     
+ Misses      37324    37320    -4     
- Partials     3900     3901    +1     

Flag	Coverage Δ		*Carryforward flag
go	50.66% <100.00%> (+0.01%)
integration	30.68% <ø> (ø)		Carriedforward from 15afbaf
storybook	30.34% <ø> (ø)		Carriedforward from 15afbaf
typescript	54.26% <ø> (ø)		Carriedforward from 15afbaf
unit	34.67% <ø> (ø)		Carriedforward from 15afbaf

*This pull request uses carry forward flags. Click here to find out more.

Impacted Files	Coverage Δ
enterprise/internal/campaigns/reconciler/plan.go	71.11% <100.00%> (+3.39%)
...nal/campaigns/resolvers/changeset_apply_preview.go	65.18% <0.00%> (+0.74%)

Created by: sourcegraph-bot

Notifying subscribers in CODENOTIFY files for diff 15afbaf1a1cbf82c88c9cc844d5f7a8699bbde3f...36a74800f5f4025d63fb6698d0a5bef03d7f27b5.

Notify	File(s)
@LawnGnome	enterprise/internal/campaigns/reconciler/plan.go enterprise/internal/campaigns/reconciler/plan_test.go