Refactor: Update GH Action

[Pathan-Amaankhan]

Description

• Recently WordPress started using SVN credentials instead of WordPress credentials for plugin release. Our GH Action still uses WordPress credentials to release the plugin, which needs to be updated with SVN credentials.

GH action that needs to be updated: https://github.com/rtCamp/nginx-helper/blob/master/.github/workflows/create.yml
Prior art (for reference): https://github.com/10up/action-wordpress-plugin-deploy/blob/develop/examples/deploy-on-pushing-a-new-tag.yml

WordPress doc Refs:

• https://make.wordpress.org/meta/handbook/tutorials-guides/svn-access/#do-i-need-to-use-a-svn-password
• https://developer.wordpress.org/plugins/wordpress-org/how-to-use-subversion/

Actionable items

• Replace WORDPRESS_USERNAME & WORDPRESS_PASSWORD in GH action with SVN_USERNAME & SVN_PASSWORD.

cc: @dhawalepranav @joelabreo227