For anybody else stumbling onto this in 2025, the answer from @ItalyPaleAle is still relevant but the certificate being used for that has been being changed. As per the docs at https://learn.microsoft.com/en-us/azure/mysql/flexible-server/concepts-root-certificate-rotation

To maintain our security and compliance standards, we start changing the root certificates for Azure Database for MySQL Flexible Server after September 1, 2025.

The current root certificate DigiCert Global Root CA is replaced by two new root certificates:

• DigiCert Global Root G2

• Microsoft RSA Root Certificate Authority 2017

The doc recommends to create a combined pem file with all 3 certs (including the now removed one), and using that. The details and downloads to these are available in the link above.