Incompatible with Project Isolation

[paulhundal-toast]

The current implementation of the plugin is not compatible with isolated projects.

    - [error] Project `:` cannot access `Project.file` functionality on subprojects
        - Exception at `com.squareup.invert.InvertGradlePlugin.hasBuildGradleFile(InvertGradlePlugin.kt:81)`
org.gradle.api.InvalidUserCodeException: Project ':' cannot access 'Project.file' functionality on subprojects
	at org.gradle.internal.cc.impl.ProblemReportingCrossProjectModelAccess$ProblemReportingProject.file(ProblemReportingCrossProjectModelAccess.kt:183)
	at com.squareup.invert.InvertGradlePlugin.hasBuildGradleFile(InvertGradlePlugin.kt:81)
	at com.squareup.invert.InvertGradlePlugin.shouldRegisterOnSubproject(InvertGradlePlugin.kt:74)
	at com.squareup.invert.InvertGradlePlugin.apply$lambda$7$lambda$5(InvertGradlePlugin.kt:38)
	at com.squareup.invert.InvertGradlePlugin.apply$lambda$7$lambda$6(InvertGradlePlugin.kt:36)