In BoringSSL, the order of preferred ciphers depends on whether or not the system supports hardware accelerated AES. (See: https://boringssl.googlesource.com/boringssl/+/refs/heads/master/ssl/ssl_cipher.c#1415)

The main.openssl_6975 MariaDB test checks which cipher is negotiated, and always expects ECDHE-RSA-AES256-GCM-SHA384, which is the preferred cipher when hardware acceleration is available. When running on machines without hardware acceleration (such as, for instance, under Memory Sanitizer), the preferred cipher in BoringSSL is ECDHE-RSA-CHACHA20-POLY1305.