fix: docker pull fallback on linux amd64 for apple silicon

[sevbch]

Context

What has been done

Validation

PR check list

• [ ] As much as possible, the changes include tests (unit and/or functional)
• [ ] If the changes affect the end user (new feature, behavior change, bug fix) then the PR has a changelog entry (see doc/dev/getting-started.md). If the changes do not affect the end user, then the skip-changelog label has been added to the PR.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 90.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 91.88%. Comparing base (bc4777c) to head (c8835dd). Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
ggshield/verticals/secret/docker.py	90.00%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1104      +/-   ##
==========================================
- Coverage   91.89%   91.88%   -0.01%     
==========================================
  Files         144      144              
  Lines        6094     6102       +8     
==========================================
+ Hits         5600     5607       +7     
- Misses        494      495       +1     

Flag	Coverage Δ
unittests	91.88% <90.00%> (-0.01%)	:arrow_down:

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