docs: replace php with PHP

Author: kenjis

user_guide_src/source/installation/upgrade_configuration.rst

@@ -25,7 +25,7 @@ Upgrade Guide
 1. You have to change the values in the default CI4 config files according to the
    changes in the CI3 files. The config names are pretty much the same as in CI3.
 2. If you are using custom config files in your CI3 project you have to create those
-   files as new php classes in your CI4 project in ``app/Config/``. These classes
+   files as new PHP classes in your CI4 project in ``app/Config/``. These classes
    should be in the ``Config`` namespace and should extend ``CodeIgniter\Config\BaseConfig``.
 3. Once you have created all custom config classes, you have to copy the variables
    from the CI3 config into the new CI4 config class as public class properties.

user_guide_src/source/tutorial/static_pages.rst

@@ -66,7 +66,7 @@ methods and variables defined in the ``CodeIgniter\Controller`` class
 (*system/Controller.php*).
 
 The **controller is what will become the center of every request** to
-your web application. Like any php class, you refer to
+your web application. Like any PHP class, you refer to
 it within your controllers as ``$this``.
 
 Now that you've created your first method, it's time to make some basic page