opgpcard: Make shebang system independent

tools/cargo-test-in-docker

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 #
 # Run this to run opgpcard (tools directory) test suite inside a
 # Docker container with a virtual smartcard running. The test suite

tools/subplot/test-in-docker.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 #
 # Run "cargo test" inside a Docker container with virtual cards
 # installed and running. This will allow at least rudimentary testing