Mark FooConvert tested with WordPress 7.1

[foo-bender]

Summary

• update the WordPress.org Tested up to value from 7.0 to 7.1
• no executable plugin code, stable tag, or release artifacts changed

Verification

• tested FooConvert 2.1.6 on WordPress 7.1-RC1 in a live sandbox
• created a Cookie Consent Bar from a template in the WordPress 7.1 iframe editor
• edited button content, published, reopened, and verified persistence
• verified the dashboard and popup settings/display-rule surfaces loaded without fatal errors
• git diff --check
• exact one-file / one-line metadata assertion
• static secret scan
• independent review

Release scope

Metadata only. This PR does not merge, tag, package, deploy, or publish to WordPress.org SVN.