Changes to any file not in a monorepo package cause ALL packages to rebuild when using --since

[dobesv]

Package

lage

Describe the bug

When using --since, if you change a file that isn't in a package (e.g. README.md or CHANGELOG.md) and you are using --since to avoid rebuiling unaffected packages, it considers all packages as affected by that change.

To Reproduce

1. Have a monorepo setup with some different packages that don't all depend on on another
2. Have a file at the monorepo root (e.g. README.md)
3. Edit the file at the monorepo root and a file in a package that not all the packages depend on
4. Run lage build --since origin/HEAD or similar to try and only build packages affected by the change
5. Notice whether it only builds affected packages or builds ALL packages.

Expected behavior

If I use --since then only the dependsOn, inputs, and so on as configured in lage, plus its dependency graph detection from yarn.lock should be used to figure out the affected packages. Changes to documention, build scripts, that have nothing to do with the code being built should not cause a rebuild.

Environment/Troubleshooting

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