fix: avoid hardcoded (ba)sh path in helper scripts.

Prior to this commit some helper scripts used hardcoded paths to
`/bin/sh` and `/bin/bash` in script shebangs. This will error on systems
that don't place `bash` in `/bin/` (e.g. NixOS).

This commit updates the scripts to use `/usr/bin/env` to find `bash`
based on the user's `$PATH`. This has better portability and allows the
scripts to run without err (or specifying an interpreter explicitly) on
systems with atypical `bash` installs.

admin/bench-measure.mk

@@ -1,6 +1,6 @@
 RECORD=perf record -F2000 --call-graph dwarf,16000 --
 FLAMEGRAPH=perf script | ~/FlameGraph/stackcollapse-perf.pl | ~/FlameGraph/flamegraph.pl >
-MEMUSAGE=/usr/bin/time -f %M
+MEMUSAGE=/usr/bin/env time -f %M
 
 perf: ./target/release/examples/bench
 	$(RECORD) ./target/release/examples/bench bulk TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256

admin/coverage

@@ -1,4 +1,6 @@
-#!/bin/bash -e
+#!/usr/bin/env bash
+
+set -e
 
 source <(cargo llvm-cov show-env --export-prefix)
 cargo llvm-cov clean --workspace

admin/pull-readme

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/usr/bin/env sh
 # Extract the introductory documentation into the README.md
 
 set -e

admin/pull-usage

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/usr/bin/env sh
 # Extract the example usage into README.md
 
 set -e

bogo/fetch-and-build

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 set -ex
 

bogo/regen-certs

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 set -e
 

bogo/runme

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 # This script fetches, builds, and runs the BoringSSL
 # TLS test tool ('BoGo') against rustls.

test-ca/build-a-pki.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/usr/bin/env sh
 
 set -xe
 

trytls/runme

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/usr/bin/env sh
 
 # This script fetches, builds, and runs the TryTLS
 # TLS test tool against rustls.  The rustls-TryTLS test stub is