Rollup merge of #120203 - rowan-sl:usr-bin-env-bash, r=compiler-errors

Replace `#!/bin/bash` with `#!/usr/bin/env bash` in rust-installer tests

This allows the rust-installer tests to pass on NixOS

This change has [already been made](https://github.com/rust-lang/rust/commit/302ad2175d938a5307dd34779e20aada691fd28a) for the actual installer, it appears that the tests were just forgotten.

src/tools/rust-installer/test.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 set -e -u