op-challenger: Use target platform for kona docker image.

[ajsutton]

Description

Fixes the arm op-challenger docker image which previously was including an amd64 kona-host binary incorrectly.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 0.00%. Comparing base (260f36e) to head (633d290).
Report is 7 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff              @@
##           develop   #13251       +/-   ##
============================================
- Coverage    45.76%        0   -45.77%     
============================================
  Files          926        0      -926     
  Lines        79531        0    -79531     
  Branches      1133        0     -1133     
============================================
- Hits         36400        0    -36400     
+ Misses       40468        0    -40468     
+ Partials      2663        0     -2663     

Flag	Coverage Δ
cannon-go-tests-32	?
cannon-go-tests-64	?
contracts-bedrock-tests	?

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see 926 files with indirect coverage changes