[Scripts] Fix a Shebang in mono-test-install for freeBSD

scripts/mono-test-install

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 #
 # Does various checks for people that we can use to diagnose
 # an end user installation
@@ -174,4 +174,4 @@ if mcs $temp_cs >& /dev/null; then
 else
     echo Failed to compile sample test program, your installation is broken
     exit 1
-fi
+fi