minor #33194 [Console] Fix incomplete output mock (derrabus)

This PR was merged into the 4.3 branch.

Discussion
----------

[Console] Fix incomplete output mock

| Q             | A
| ------------- | ---
| Branch?       | 4.3
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | N/A
| License       | MIT
| Doc PR        | N/A

Backport from #33153. Merging this up should fix the broken tests on 4.4 and master.

Commits
-------

6ecbcf6f22 [Console] Fix incomplete output mock.

src/Symfony/Component/Console/Tests/Helper/DumperTest.php

@@ -37,7 +37,10 @@ class DumperTest extends TestCase
      */
     public function testInvoke($variable)
     {
-        $dumper = new Dumper($this->getMockBuilder(OutputInterface::class)->getMock());
+        $output = $this->getMockBuilder(OutputInterface::class)->getMock();
+        $output->method('isDecorated')->willReturn(false);
+
+        $dumper = new Dumper($output);
 
         $this->assertDumpMatchesFormat($dumper($variable), $variable);
     }