minor symfony#16507 [ci] Tmp force phpunit/phpunit-mock-objects <= 3.0.0 (nicolas-grekas)

This PR was merged into the 2.3 branch.

Discussion
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[ci] Tmp force phpunit/phpunit-mock-objects <= 3.0.0

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

To make tests green again until sebastianbergmann/phpunit-mock-objects#272 or sebastianbergmann/phpunit-mock-objects#268 is merged+tagged.

Commits
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1b428df [ci] Tmp force phpunit/phpunit-mock-objects <= 3.0.0

Author: nicolas-grekas

phpunit

@@ -49,6 +49,7 @@ if (!file_exists("$PHPUNIT_DIR/phpunit-$PHPUNIT_VERSION/phpunit") || md5_file(__
     $zip->close();
     chdir("phpunit-$PHPUNIT_VERSION");
     passthru("$COMPOSER remove --no-update symfony/yaml");
+    passthru("$COMPOSER require --no-update phpunit/phpunit-mock-objects \"<=3.0.0\"");
     passthru("$COMPOSER require --dev --no-update symfony/phpunit-bridge \">=2.8@dev\"");
     passthru("$COMPOSER install --prefer-source --no-progress --ansi");
     file_put_contents('phpunit', <<<EOPHP