Fix test to check STDERR for progress bar output

Progress bars in WP-CLI output to STDERR, not STDOUT. Updated tests to check STDERR for "Updating" message from progress bar. This fixes the test that was failing because it was checking the wrong output stream.

Co-authored-by: swissspidy <841956+swissspidy@users.noreply.github.com>

Author: Copilot

features/search-replace.feature

@@ -1400,7 +1400,7 @@ Feature: Do global search/replace
     And I run `wp option set test_url 'Visit http://example.com for more'`
 
     When I run `wp search-replace http://example.com http://example.org --precise`
-    Then STDOUT should contain:
+    Then STDERR should contain:
       """
       Updating
       """
@@ -1415,7 +1415,7 @@ Feature: Do global search/replace
       """
       Checking:
       """
-    And STDOUT should not contain:
+    And STDERR should not contain:
       """
       Updating
       """