application-services build is missing rustc in PATH

In a nightly and testbuild, I see:

> Task :full-megazord:preBuild UP-TO-DATE
> Task :full-megazord:preReleaseBuild UP-TO-DATE
> Task :full-megazord:compileReleaseAidl NO-SOURCE
> Task :generateLinkerWrapper
> Task :full-megazord:cargoBuildArm FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':full-megazord:cargoBuildArm'.
> A problem occurred starting process 'command 'rustc''

I believe this is because we export the rust path:

export PATH=/var/tmp/dist/fenix-rust/bin:$PATH

while on disk we have:

debug-application-services$ ls /var/tmp/dist/
android-toolchain  application-services  fenix-as-rust  python

That is since #40115 (closed).