gnupg2: update to 2.5.21

gnupg2: update to 2.5.21

New and extended features:
- gpg, gpgsm: use a partial file on decryption, remove on failure
  (disable with --compatibility-flags=no-partial-file-guard)
- gpg: use the INT_RCP_FPR subpacket in revocation signatures
- create a pkgversioninfo.txt file when building with the speedo build
  system

Bug fixes:
- gpg: fixed a potential use-after-free in batch key generation when
  handling the keyserver URL option
- gpgsm: fixed a regression in gpgsm_verify with expired certificates
- gpgsm: require a minimum tag length for GCM decryption
  (CVE-2026-34182)
- scd: limit the size of returned APDU objects from faulty cards; fixed
  the condition to retrieve ATR

Signed-off-by: Daniel Golle <redacted>