Allow prevent_cross_joins to be used directly in tests

What does this MR do?

This MR makes 2 improvements in our efforts towards moving ci_* tables to a separate database:

1. It fixes a cross-join in ::Ci::Build.with_project_and_metadata
2. It introduces a new helper method to use in tests ::Database::PreventCrossJoins.prevent_cross_joins that can be used to wrap an isolated piece of code and validate that it is not doing any cross-joins. This helper is just a small addition on top of the validation logic that was already implemented in !67019 (merged)

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How to setup and validate locally (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• [-] I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
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• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
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• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
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Security

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• Label as security and @ mention @gitlab-com/gl-security/appsec
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