perf-tests: #!/bin/bash -> #!/usr/bin/env bash

I couldn't run the performance tests on my machines due to a hardcoded
bash path. Use env for finding bash in weird systems like NixOS.

Signed-off-by: William Casarin <jb55@jb55.com>

performance-test/M00-new.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 test_description='notmuch new'
 

performance-test/M01-dump-restore.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 test_description='dump and restore'
 

performance-test/M02-show.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 test_description='show'
 

performance-test/M03-search.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 test_description='search'
 

performance-test/M04-reply.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 test_description='search'
 

performance-test/M05-reindex.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 test_description='reindex'
 

performance-test/M06-insert.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 test_description='search'
 

performance-test/T00-new.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 test_description='notmuch new'
 

performance-test/T01-dump-restore.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 test_description='dump and restore'
 

performance-test/T02-tag.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 test_description='tagging'
 

performance-test/T03-reindex.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 test_description='reindexing'
 

performance-test/T04-thread-subquery.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 test_description='thread subqueries'