[Process] Fix backwards compatibility for invalid commands

Process.php

@@ -358,6 +358,11 @@ public function start(?callable $callback = null, array $env = []): void
 
         try {
             $process = @proc_open($commandline, $descriptors, $this->processPipes->pipes, $this->cwd, $envPairs, $this->options);
+
+            // Ensure array vs string commands behave the same
+            if (!$process && \is_array($commandline)) {
+                $process = @proc_open('exec '.$this->buildShellCommandline($commandline), $descriptors, $this->processPipes->pipes, $this->cwd, $envPairs, $this->options);
+            }
         } finally {
             if ($this->ignoredSignals && \function_exists('pcntl_sigprocmask')) {
                 // we restore the signal mask here to avoid any side effects

Tests/ProcessTest.php

@@ -72,13 +72,8 @@ public function testInvalidCwd()
      */
     public function testInvalidCommand(Process $process)
     {
-        try {
-            $this->assertSame('\\' === \DIRECTORY_SEPARATOR ? 1 : 127, $process->run());
-        } catch (ProcessStartFailedException $e) {
-            // An invalid command might already fail during start since PHP 8.3 for platforms
-            // supporting posix_spawn(), see https://github.com/php/php-src/issues/12589
-            $this->assertStringContainsString('No such file or directory', $e->getMessage());
-        }
+        // An invalid command should not fail during start
+        $this->assertSame('\\' === \DIRECTORY_SEPARATOR ? 1 : 127, $process->run());
     }
 
     public function invalidProcessProvider()