tree-wide: replace /bin/bash with /usr/bin/env bash

The latter is more portable, while the former only works on systems
where /bin/bash exists (or is symlinked appropriately).

bin/use-deadlock-detector

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 if [[ ! -z $(git status --short --untracked-files=no) ]]; then
    echo "Detected uncommitted changes - commit before running this"