Don't use transient values when doing wp plugin|theme list

This changes the default behavior to always check wordpress.org for the
latest information when doing wp plugin|theme list unless the existing
`--skip-update-check` flag is passed.

Author: mrsdizzie

features/plugin.feature

@@ -317,6 +317,27 @@ Feature: Manage WordPress plugins
       Automattic
       """
 
+    When I run `wp eval 'echo get_site_transient("update_plugins")->last_checked;'`
+    And save STDOUT as {LAST_UPDATED}
+
+    When I run `wp plugin list --skip-update-check`
+    Then STDOUT should not be empty
+
+    When I run `wp eval 'echo get_site_transient("update_plugins")->last_checked;'`
+    Then STDOUT should be:
+      """
+      {LAST_UPDATED}
+      """
+
+    When I run `wp plugin list`
+    Then STDOUT should not be empty
+
+    When I run `wp eval 'echo get_site_transient("update_plugins")->last_checked;'`
+    Then STDOUT should not contain:
+      """
+      {LAST_UPDATED}
+      """
+
   Scenario: List plugin by multiple statuses
     Given a WP multisite install
     And a wp-content/plugins/network-only.php file:

features/theme.feature

@@ -233,6 +233,34 @@ Feature: Manage WordPress themes
       | name      | status   | update |
       | astra     | inactive | none   |
 
+
+  Scenario: Doing wp theme list does a force check by default, deleting any existing transient values
+    Given a WP install
+
+    When I run `wp theme list`
+    Then STDOUT should not be empty
+
+    When I run `wp eval 'echo get_site_transient("update_themes")->last_checked;'`
+    And save STDOUT as {LAST_UPDATED}
+
+    When I run `wp theme list --skip-update-check`
+    Then STDOUT should not be empty
+
+    When I run `wp eval 'echo get_site_transient("update_themes")->last_checked;'`
+    Then STDOUT should be:
+      """
+      {LAST_UPDATED}
+      """
+
+    When I run `wp theme list`
+    Then STDOUT should not be empty
+
+    When I run `wp eval 'echo get_site_transient("update_themes")->last_checked;'`
+    Then STDOUT should not contain:
+      """
+      {LAST_UPDATED}
+      """
+
   Scenario: Install a theme when the theme directory doesn't yet exist
     Given a WP install
     And I run `wp theme delete --all --force`

src/WP_CLI/CommandWithUpgrade.php

@@ -543,6 +543,7 @@ protected function _list( $_, $assoc_args ) {
 
 		// Force WordPress to check for updates if `--skip-update-check` is not passed.
 		if ( false === (bool) Utils\get_flag_value( $assoc_args, 'skip-update-check', false ) ) {
+			delete_site_transient( $this->upgrade_transient );
 			call_user_func( $this->upgrade_refresh );
 		}