Apply Fix to Layer class methods correctly

[ByteOtter]

What this PR does / why we need it:

Places the else block in __delitem__() properly instead of __getitem__()

Which issue(s) this PR fixes:
Fixes n/A

Special notes for your reviewer:

Release note:

bugfix developer
* Fix misplaced else block in __getitem__() and moves it to __delitem__() to fix always raising KeyError

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.23%. Comparing base (4729eb7) to head (537f2c2).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/gardenlinux/oci/layer.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #167   +/-   ##
=======================================
  Coverage   85.23%   85.23%           
=======================================
  Files          27       27           
  Lines        1226     1226           
=======================================
  Hits         1045     1045           
  Misses        181      181           

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