Update minimum version to follow our L-4 standard

Author: dkotter

.github/workflows/e2e.yml

@@ -27,7 +27,7 @@ jobs:
       matrix:
         core:
           - {name: 'WP latest', version: 'latest'}
-          - {name: 'WP minimum', version: 'WordPress/WordPress#6.6'}
+          - {name: 'WP minimum', version: 'WordPress/WordPress#6.4'}
           - {name: 'WP trunk', version: 'WordPress/WordPress#master'}
 
     steps:

mailchimp.php

@@ -5,7 +5,7 @@
  * Description:       Add a Mailchimp signup form block, widget or shortcode to your WordPress site.
  * Text Domain:       mailchimp
  * Version:           1.7.0
- * Requires at least: 6.6
+ * Requires at least: 6.4
  * Requires PHP:      7.0
  * PHP tested up to:  8.3
  * Author:            Mailchimp

phpcs-compat.xml

@@ -12,6 +12,6 @@
 	<exclude-pattern>*/node_modules/*</exclude-pattern>
 	<exclude-pattern>*/vendor/*</exclude-pattern>
 
-	<config name="minimum_supported_wp_version" value="6.6"/>
+	<config name="minimum_supported_wp_version" value="6.4"/>
 	<config name="testVersion" value="7.0-"/>
 </ruleset>

phpcs.xml

@@ -6,7 +6,7 @@
 
 	<exclude-pattern>*/tests/*</exclude-pattern>
 
-	<config name="minimum_supported_wp_version" value="6.6"/>
+	<config name="minimum_supported_wp_version" value="6.4"/>
 	<config name="testVersion" value="7.0-"/>
 
 	<!-- Exclude the PHPCompatibilityWP ruleset -->