add(scan): Run scans_for_new_key and scan_subscribe_results tests in CI

[arya2]

Motivation

We want to run these tests in CI.

Closes #8274.
Closes #8259.

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Solution

• Add the tests to entrypoint.sh
• Add the tests to GCP integration test workflow

Review

Anyone can review.

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Follow Up Work

• Improve scans_for_new_key test #8236

[arya2]

The tests pass, but it's exiting with an exit code of 1 somehow: https://github.com/ZcashFoundation/zebra/actions/runs/7923158455/job/21632648787?pr=8275#step:15:261

It seems to emit an exit code of 0 locally.

There's also an unrelated port conflict in the latest run of 'Test All'

[arya2]

I'll unify these tests for #8286 first and re-open this PR to add the new test to CI.