chore(cli-integ): pin integ test Node version to 24.19

[mrgrain]

Integ tests are failing on every synth with TypeError: Invalid URL since GitHub runners started resolving node-version: lts/* to Node.js 24.20.0 (see the init-templates failures). Node 24.20.0 ships the ada 4.0.0 URL parser, which correctly rejects the invalid URLs jsonschema builds while resolving local $refs during manifest validation (enabled in integ tests via TESTING_CDK=1). The failing code lives in the published aws-cdk-lib, which bundles @aws-cdk/cloud-assembly-schema with the unfixed jsonschema — so the patch merged in #1945 cannot reach it.

This pins the integ test matrix Node version to 24.19 until a fixed @aws-cdk/cloud-assembly-schema is released and re-bundled by aws-cdk-lib, at which point the pin should be reverted to lts/*. The prepare/build job keeps lts/* since it builds this repo, which already carries the patch; the tool-integrations job keeps its existing Node 20 override.

Checklist

• This change contains a major version upgrade for a dependency and I confirm all breaking changes are addressed
  • Release notes for the new version:

---

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

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.30%. Comparing base (d4cb6e9) to head (da4a669).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1949      +/-   ##
==========================================
- Coverage   91.33%   91.30%   -0.04%     
==========================================
  Files          79       79              
  Lines       12164    12164              
  Branches     1721     1719       -2     
==========================================
- Hits        11110    11106       -4     
- Misses       1019     1023       +4     
  Partials       35       35              

Flag	Coverage Δ
suite.unit	91.30% <ø> (-0.04%)	⬇️

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