chore(ec2): fix an incorrect import of ValidationError

[Tietew]

Reason for this change

I'd missed an incorrect import of ValidationError in #33619

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.38%. Comparing base (160da34) to head (4a50836).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #33897   +/-   ##
=======================================
  Coverage   82.38%   82.38%           
=======================================
  Files         120      120           
  Lines        6938     6938           
  Branches     1170     1170           
=======================================
  Hits         5716     5716           
  Misses       1119     1119           
  Partials      103      103           

Flag	Coverage Δ
suite.unit	82.38% <ø> (ø)

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Components	Coverage Δ
packages/aws-cdk	∅ <ø> (∅)
packages/aws-cdk-lib/core	82.38% <ø> (ø)

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AWS CodeBuild CI Report

• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: 4a50836
• Result: SUCCEEDED
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