fix: set the default block to stackable/text

[Arukuen]

fixes #3273

Is there a better place where can we set the default block aside aside from editor-loader?

[github-actions[bot]]

🤖 Pull request artifacts

file	commit
pr3275-stackable-3275-merge.zip	6ad1f88f3d83f8689542f6d9d931f654acd0f99d

[github-actions[bot]]

Try this Pull Request in the WordPress playground: https://playground.wordpress.net/?mode=seamless#{"landingPage":"/wp-admin/post-new.php?post_type=page","preferredVersions":{"php":"latest","wp":"latest"},"steps":[{"step":"login","username":"admin","password":"password"},{"step":"installPlugin","pluginZipFile":{"resource":"url","url":"https://raw.githubusercontent.com/gambitph/Stackable/artifacts/pr3275-stackable-3275-merge.zip"}}]}