Release v1.28.0

What's Changed

• Revert "Trim some unused XN_FLAG_* values" by @samuel40791765 in #1582
• [EC] Unify point doubling for P-256/384/521 by @dkostic in #1567
• Enable x86_64 AES-GCM proof in AWS-LC CI by @pennyannn in #1592
• Update the formal verification section in README by @pennyannn in #1570
• fix X509V3_EXT_METHODs for ocsp nonce extension by @samuel40791765 in #1603
• Prepare for release v1.28.0 by @samuel40791765 in #1604
• CI update for ubuntu 24.04 by @justsmth in #1599
• Upstream merge 2024 05 10 by @nebeid in #1590

Full Changelog: v1.27.0...v1.28.0