integration: Fix running on systems with sparse /bin

`/bin/bash` is an unstable path that doesn't exist on all distributions,
or may point to an unwanted version of bash. Here we switch to relying on
pulling Bash from a users `PATH` to cover those cases.

This fixes running integration tests on NixOS.

Signed-off-by: Danielle Lancashire <dani@builds.terrible.systems>

Author: endocrimes

tests/integration.rs

@@ -1009,7 +1009,7 @@ mod integration_tests {
         if cfg!(target_os = "windows") {
             String::from("powershell.exe")
         } else {
-            String::from("/bin/bash")
+            String::from("bash")
         }
     }