fix: Failing Docker Image workflow

[davidgamez]

Summary:

GitHub Docker Image step is failing in the master branch after #1382 was merged with the following message:

...
FAILURE: Build failed with an exception.

* What went wrong:
Task 'testReport' not found in root project 'gtfs-validator'.
...

Example Github action: https://github.com/MobilityData/gtfs-validator/actions/runs/4669878286/jobs/8268916282

In this PR the gradle task testReport is replaced by the testAggregateTestReport in the test step of docker workflow.

Expected behavior:

Github docker workflow successfully runs.

Please make sure these boxes are checked before submitting your pull request - thanks!

• Run the unit tests with gradle test to make sure you didn't break anything
• Format the title like "feat: [new feature short description]". Title must follow the Conventional Commit Specification(https://www.conventionalcommits.org/en/v1.0.0/).
• Linked all relevant issues
• Include screenshot(s) showing how this pull request works and fixes the issue(s)

[davidgamez]

Docker Image workflow passed, reference https://github.com/MobilityData/gtfs-validator/actions/runs/4700481725/jobs/8335226732?pr=1386

[github-actions]

✅ Rule acceptance tests passed.
New Errors: 0 out of 1425 datasets (~0%) are invalid due to code change, which is less than the provided threshold of 1%.
Dropped Errors: 0 out of 1425 datasets (~0%) are invalid due to code change, which is less than the provided threshold of 1%.
New Warnings: 0 out of 1425 datasets (~0%) are invalid due to code change, which is less than the provided threshold of 1%.
Dropped Warnings: 0 out of 1425 datasets (~0%) are invalid due to code change, which is less than the provided threshold of 1%.
0 out of 1425 sources (~0 %) are corrupted.
Commit: bb2c448
Download the full acceptance test report here (report will disappear after 90 days).
✅ Rule acceptance tests passed.

[welcome]

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