build/deps: upgrade openssl to v3.0.20 (CVE-2026-31790)

[tyson-redpanda]

Upgrades the base OpenSSL build from 3.0.19 to 3.0.20 to fix CVE-2026-31790
(SNYK-UNMANAGED-OPENSSL-15928863): Improper Check for Unusual or Exceptional
Conditions in the RSASVE encapsulation path — an invalid RSA public key causes
uninitialized memory to be used as ciphertext output.

The openssl-fips build (3.0.9) is intentionally unchanged: it produces only
fips.so (the NIST CMVP-validated provider module), which does not contain the
vulnerable EVP encapsulation code. No validated fix version exists for the 3.0.x
FIPS provider; that finding is tracked separately.

The corresponding fix for dev and v26.1.x (OpenSSL 3.5.6) is in
#30238.

No vtools PR is required — this branch references OpenSSL via direct GitHub
release URL.

Backports Required

• none - this is a backport

Release Notes

Bug Fixes

• Upgraded OpenSSL from 3.0.19 to 3.0.20 to address CVE-2026-31790, which could allow an attacker supplying a malformed RSA public key to trigger use of uninitialized memory during RSA key encapsulation.

FIXES=CORE-16121