Bump premailer from 1.11.1 to 1.12.1 (#14437)

Bumps [premailer](https://github.com/premailer/premailer) from 1.11.1 to 1.12.1.
- [Release notes](https://github.com/premailer/premailer/releases)
- [Changelog](https://github.com/premailer/premailer/blob/master/CHANGELOG.md)
- [Commits](https://github.com/premailer/premailer/compare/v1.11.1...v1.12.1)

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Gemfile.lock

@@ -418,7 +418,7 @@ GEM
     pghero (2.6.0)
       activerecord (>= 5)
     pkg-config (1.4.1)
-    premailer (1.11.1)
+    premailer (1.12.1)
       addressable
       css_parser (>= 1.6.0)
       htmlentities (>= 4.0.0)