Update to PHP 7.4 and MariaDB 10.4. For details, see https://pantheon.io/docs/pantheon-yml#specify-a-version-of-mariadb

Author: Pantheon Automation

pantheon.upstream.yml

@@ -3,9 +3,13 @@
 # Override the defaults specified here in a site-specific `pantheon.yml` file.
 # For more information see: https://pantheon.io/docs/pantheon-upstream-yml
 api_version: 1
-php_version: 7.2
+php_version: 7.4
 drush_version: 8
 
+# See https://pantheon.io/docs/pantheon-yml#specify-a-version-of-mariadb
+database:
+  version: 10.4
+
 # See https://pantheon.io/docs/pantheon-yml/#enforce-https--hsts for valid values.
 enforce_https: transitional