[Rel-Eng]: Change from '/bin/bash' to '/usr/bin/env bash' in the down…

…load script

Modifies the top shebang from being #!/bin/bash to #!/usr/bin/env bash
in the 'download-cabal-install-release-binaries.sh'

The later seems more portable as learned from the PR review comments.

scripts/release/download-cabal-install-release-binaries.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 # A script to download the release binary files for a given cabal release
 # from upstream "downlods.haskell.org".