Tests: First pass at using `assertSame()` instead of `assertEquals()` in most of the unit tests.

This ensures that not only the return values match the expected results, but also that their type is the same.

Going forward, stricter type checking by using `assertSame()` should generally be preferred to `assertEquals()` where appropriate, to make the tests more reliable.

Props johnbillion, jrf, SergeyBiryukov.
See #38266.
Built from https://develop.svn.wordpress.org/trunk@48937


git-svn-id: http://core.svn.wordpress.org/trunk@48699 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.6-alpha-48931';
+$wp_version = '5.6-alpha-48937';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.