Avoid recursing when installing a project to a subproject via copytree

[djbelknap]

resolves #9719

Problem

When installing a local package that contains the current project as a subfolder (like the integration_tests project in dbt-utils), if the symlink fails the copytree recursively copies the current project repeatedly until the path length limit is reached.

Solution

Use the ignore parameter of copytree to ignore the current project's packages directory to avoid repeated recursion.

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR (Let me know if you'd like a test specific to this fix)
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX
• This PR includes type annotations for new and modified functions

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