Fixed run-tests.php for PHP 7.2

Flexible heredoc syntax is only available since PHP 7.3.

Closes GH-5444.

Author: flavioheleno

run-tests.php

@@ -2748,7 +2748,7 @@ function run_test($php, $file, $env)
         }
 
         // write .sh
-        if (strpos($log_format, 'S') !== false && file_put_contents($sh_filename, <<<SH
+        $sh_script = <<<SH
 #!/bin/sh
 
 case "$1" in
@@ -2765,7 +2765,8 @@ function run_test($php, $file, $env)
     {$cmd}
     ;;
 esac
-SH, FILE_BINARY) === false) {
+SH;
+        if (strpos($log_format, 'S') !== false && file_put_contents($sh_filename, $sh_script, FILE_BINARY) === false) {
             error("Cannot create test shell script - $sh_filename");
         }
         chmod($sh_filename, 0755);