Fix unit tests on Android (#10224)

# Description

* The path to the binaries for tests is slightly incorrect. It is
missing the build target when it is set with the `CARGO_BUILD_TARGET`
environment variable. For example, when `CARGO_BUILD_TARGET` is set to
`aarch64-linux-android`, the path to the `nu` binary is:

  `./target/aarch64-linux-android/debug/nu`

  rather than

  `./target/debug/nu`

This is common on Termux since the default target that rustc detects can
cause problems on some projects, such as [python's `cryptography`
package](https://github.com/pyca/cryptography/issues/7248).
  
This technically isn't a problem specific to Android, but is more likely
to happen on Android due to the latter.
* Additionally, the existing variable named `NUSHELL_CARGO_TARGET` is in
fact the profile, not the build target, so this was renamed to
`NUSHELL_CARGO_PROFILE`. This change is included because without the
rename, the build system would be using `CARGO_BUILD_TARGET` for the
build target and `NUSHELL_CARGO_TARGET` for the build profile, which is
confusing.
* `std path add` tests were missing `android` test

# User-Facing Changes

For those who would like to build nushell on Termux, the unit tests will
pass now.

scripts/coverage-local.sh

@@ -17,7 +17,7 @@ REPO_ROOT=$(dirname $DIR)
 # Some of the internal tests rely on the exact cargo profile
 # (This is somewhat criminal itself)
 # but we have to signal to the tests that we use the `ci` `--profile`
-export NUSHELL_CARGO_TARGET=ci
+export NUSHELL_CARGO_PROFILE=ci
 
 # Manual gathering of coverage to catch invocation of the `nu` binary.
 # This is relevant for tests using the `nu!` macro from `nu-test-support`