Fix Pro URL in contact-buttons-render-base

[szepeviktor]

PR Checklist

• The commit message follows our guidelines: https://github.com/elementor/elementor/blob/master/.github/CONTRIBUTING.md

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe: fix an URL

Summary

Without the trailing slash it produces a redirect.

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[szepeviktor]

@elementorbot stop

[toineenzo]

@elementorbot stop

Why are you arguing with a bot lol