Plugin is passing RUSTC_BOOTSTRAP=1 to build scripts

[null-dev]

Environment

• IntelliJ Rust plugin version: 0.4.182.4996-222
• Rust toolchain version: 1.63.0 (4b91a6ea7 2022-08-08) x86_64-unknown-linux-gnu
• IDE name and version: CLion 2022.2.4 (CL-222.4345.21)
• Operating system: Linux 6.0.7-arch1-1
• Macro expansion: enabled

Problem description

The plugin is passing RUSTC_BOOTSTRAP=1 to build scripts sometimes (seems to only happen when you import a project without the target directory). This breaks build scripts that probe for nightly features, see #9235 for a similar bug.

Steps to reproduce

1. Create a project with a dependency that has a build script that probes for nightly features (e.g. thiserror)
2. Close Clion/Intellij
3. Delete the target directory of the project
4. Open the project in Clion/Intellij
5. Wait for background tasks to complete
6. Attempt to build/run the project
7. The project fails to build/run.

PR that might be related but I don't think(?) is relevant: #9637