Fix CI failure while building shader crate

[Shfty]

Exits with the following:

error: couldn't load codegen backend "/home/runner/work/bevy-pbr-rust/bevy-pbr-rust/rust-gpu/target/release/librustc_codegen_spirv.so": librustc_driver-7dc221ef4086baf7.so: cannot open shared object file: No such file or directory

Initial research indicates an issue with linker paths, but adding /usr/local/lib to the PATH didn't seem to change anything. Running find against the mentioned library from the working dir turns up nothing either, so will have to run it from the root and see if it exists at all.