fix: remove temp dir if installer fails to download

[jahzielv]

For #25373

Checklist for submitter

If some of the following don't apply, delete the relevant line.

• Changes file added for user-visible changes in changes/, orbit/changes/ or ee/fleetd-chrome/changes.
  See Changes files for more information.
• Added/updated automated tests
• A detailed QA plan exists on the associated ticket (if it isn't there, work with the product group's QA engineer to add it)
• Manual QA for all new/changed functionality
• For Orbit and Fleet Desktop changes:
  • Orbit runs on macOS, Linux and Windows. Check if the orbit feature/bugfix should only apply to one platform (runtime.GOOS).
  • Manual QA must be performed in the three main OSs, macOS, Windows and Linux.
  • Auto-update manual QA, from released version of component to new version (see tools/tuf/test).

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 6 lines in your changes missing coverage. Please review.

Project coverage is 63.60%. Comparing base (6235642) to head (b1ce16f).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
orbit/pkg/installer/installer.go	33.33%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main   #25392    +/-   ##
========================================
  Coverage   63.60%   63.60%            
========================================
  Files        1626     1623     -3     
  Lines      155551   155402   -149     
  Branches     4045     4009    -36     
========================================
- Hits        98941    98848    -93     
+ Misses      48810    48754    -56     
  Partials     7800     7800            

Flag	Coverage Δ
backend	64.45% <33.33%> (+<0.01%)	⬆️

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[iansltx]

Looks reasonable. Approved once a changes file is added, and can be merged once we're out of the fleetd freeze.

[iansltx]

Will need to be merged after the fleetd freeze is lifted, but it's ready!