Merge tag 'v5.15.21' into v5.15/standard/base

This is the 5.15.21 stable release

# gpg: Signature made Sat 05 Feb 2022 01:21:14 PM EST
# gpg:                using RSA key 647F28654894E3BD457199BE38DBBDC86092693E
# gpg: Can't check signature: No public key