[phoenix_html] phoenix_html allows Cross-site Scripting in HEEx class attributes

tag.ex in Phoenix Phoenix.HTML (aka phoenix_html) before 3.0.4 allows XSS in HEEx class attributes.

References

• https://nvd.nist.gov/vuln/detail/CVE-2021-46871
• https://github.com/phoenixframework/phoenix_html/commit/62a0139fb716bcdce697f6221244bd81d321d620
• https://github.com/advisories/GHSA-j3gg-r6gp-95q2
• https://github.com/advisories/GHSA-5g2h-9x5v-5h3x