chore: update phpunit.xml to include source directory for code coverage

Author: bbsnly

phpunit.xml

@@ -2,10 +2,15 @@
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:noNamespaceSchemaLocation="vendor/phpunit/phpunit/phpunit.xsd"
          bootstrap="vendor/autoload.php"
-         colors="true"
->  <testsuites>
-    <testsuite name="Unit">
-      <directory suffix="Test.php">./tests</directory>
-    </testsuite>
-  </testsuites>
+         colors="true">
+    <testsuites>
+        <testsuite name="Unit">
+            <directory suffix="Test.php">./tests</directory>
+        </testsuite>
+    </testsuites>
+    <source>
+        <include>
+            <directory suffix=".php">src</directory>
+        </include>
+    </source>
 </phpunit>