fix(instance): snapshot list: get snapshot using image.Zone

[Mia-Cross]

#4766 introduced a bug by getting snapshots using the zone of the volume, but this field is not present for SBS snapshots in the instance API.
We should use the zone of the image instead.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 56.21%. Comparing base (5bf53e0) to head (923e0bf).
⚠️ Report is 745 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (5bf53e0) and HEAD (923e0bf). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (5bf53e0)	HEAD (923e0bf)
	2	1

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #4930       +/-   ##
===========================================
- Coverage   75.45%   56.21%   -19.24%     
===========================================
  Files         202      308      +106     
  Lines       44323    77790    +33467     
===========================================
+ Hits        33444    43731    +10287     
- Misses       9653    32656    +23003     
- Partials     1226     1403      +177     

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