Avoid accessing undefined variables in run-tests.php

The $php_cgi and $phpdbg cases here are definitely real bugs, and
caused the script to bail out under certain ini settings.

The other paths may actually be unreachable in practice, but were
highlighted by PhpStorm.

run-tests.php

@@ -1802,13 +1802,8 @@ function run_test(string $php, $file, array $env): string
     $org_file = $file;
     $orig_php = $php;
 
-    if (isset($env['TEST_PHP_CGI_EXECUTABLE'])) {
-        $php_cgi = $env['TEST_PHP_CGI_EXECUTABLE'];
-    }
-
-    if (isset($env['TEST_PHPDBG_EXECUTABLE'])) {
-        $phpdbg = $env['TEST_PHPDBG_EXECUTABLE'];
-    }
+    $php_cgi = $env['TEST_PHP_CGI_EXECUTABLE'] ?? null;
+    $phpdbg = $env['TEST_PHPDBG_EXECUTABLE'] ?? null;
 
     if (is_array($file)) {
         $file = $file[0];
@@ -2489,6 +2484,8 @@ function run_test(string $php, $file, array $env): string
         }
     }
 
+    $wanted_headers = null;
+    $output_headers = null;
     $failed_headers = false;
 
     if ($test->hasSection('EXPECTHEADERS')) {
@@ -2647,6 +2644,8 @@ function run_test(string $php, $file, array $env): string
         }
     }
 
+    $restype = [];
+
     if ($leaked) {
         $restype[] = $test->hasSection('XLEAK') ?
                         'XLEAK' : 'LEAK';