Build/Test Tools: Replace `assertInternalType()` usage in unit tests.

The `assertInternalType()` and `assertNotInternalType()` methods are deprecated in PHPUnit 8 and removed in PHPUnit 9.

While WordPress test suite currently only supports PHPUnit up to 7.5.x, this allows us to switch to newer assertions ahead of adding full support for PHPUnit 8+.

These methods introduced in PHPUnit 7.5 should be used as an alternative:

* `assertIsArray()`
* `assertIsBool()`
* `assertIsFloat()`
* `assertIsInt()`
* `assertIsNumeric()`
* `assertIsObject()`
* `assertIsResource()`
* `assertIsString()`
* `assertIsScalar()`
* `assertIsCallable()`
* `assertIsIterable()`
* `assertIsNotArray()`
* `assertIsNotBool()`
* `assertIsNotFloat()`
* `assertIsNotInt()`
* `assertIsNotNumeric()`
* `assertIsNotObject()`
* `assertIsNotResource()`
* `assertIsNotString()`
* `assertIsNotScalar()`
* `assertIsNotCallable()`
* `assertIsNotIterable()`

As WordPress currently uses PHPUnit 5.7.x to run tests on PHP 5.6, polyfills for these methods are now added to the `WP_UnitTestCase` class for PHPUnit < 7.5.

Props pbearne, jrf, dd32, SergeyBiryukov.
Fixes #53491. See #46149.
Built from https://develop.svn.wordpress.org/trunk@51331


git-svn-id: http://core.svn.wordpress.org/trunk@50940 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-alpha-51330';
+$wp_version = '5.9-alpha-51331';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.