Add PHP syntax check to steps
Add PHP syntax check to steps

Updates the CI steps to include a PHP syntax check as attempting to push
a new release has failed.

```
svn: E165001: Commit failed (details follow):
svn: E165001: Commit blocked by pre-commit hook (exit code 1) with output:

***********************************
PHP error in: cloudflare/tags/3.8.10/vendor/sebastian/diff/tests/ParserTest.php:

Parse error: Invalid body indentation level (expecting an indentation level of at least 1) in Standard input code on line 78
Errors parsing Standard input code
***********************************
```

Checking with `php -l`

```
$ php -l vendor/sebastian/diff/tests/ParserTest.php

Parse error: Invalid body indentation level (expecting an indentation level of at least 1) in vendor/sebastian/diff/tests/ParserTest.php on line 78
Errors parsing vendor/sebastian/diff/tests/ParserTest.php
```

cloudflare/Cloudflare-WordPress,cloudflare/Cloudflare-WordPress,cloudflare/Cloudflare-WordPress