Oh, I found the culprint, the confcheck tests fails with LeakSanitizer:

=================================================================
==25136==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 160 byte(s) in 2 object(s) allocated from:
    #0 0x4b94e8 in malloc (/home/ondrej/Projects/bind9/conftest+0x4b94e8)
    #1 0x7f24ebcfba5d in CRYPTO_zalloc (/usr/lib/x86_64-linux-gnu/libcrypto.so.1.1+0x16ba5d)

Indirect leak of 2104 byte(s) in 50 object(s) allocated from:
    #0 0x4b94e8 in malloc (/home/ondrej/Projects/bind9/conftest+0x4b94e8)
    #1 0x7f24ebcfba5d in CRYPTO_zalloc (/usr/lib/x86_64-linux-gnu/libcrypto.so.1.1+0x16ba5d)

Indirect leak of 416 byte(s) in 4 object(s) allocated from:
    #0 0x4b94e8 in malloc (/home/ondrej/Projects/bind9/conftest+0x4b94e8)
    #1 0x7f24ebc52cd6 in BN_MONT_CTX_new (/usr/lib/x86_64-linux-gnu/libcrypto.so.1.1+0xc2cd6)

Indirect leak of 40 byte(s) in 2 object(s) allocated from:
    #0 0x4b94e8 in malloc (/home/ondrej/Projects/bind9/conftest+0x4b94e8)
    #1 0x7f24ebc9413f in EC_GROUP_set_seed (/usr/lib/x86_64-linux-gnu/libcrypto.so.1.1+0x10413f)

SUMMARY: AddressSanitizer: 2720 byte(s) leaked in 58 allocation(s).