Revert inappropriate libmariadb stable ABI version changes

This reverts commits made on January 2023:
d204e83
d712484

In MariaDB 10.3.38 users complained that some of the software that relied on
MariaDB stopped working. This was due to functions mysql_get_client_info() and
mysql_get_client_version() which suddenly started to emit 3.1.20 and 30120
instead of the expected 10.3.38 and 100338.

The functions had been emitting the MariaDB server version for at least the past
8 years. There was no good justification to break the ABI in this way in a
stable release.

The issue with libqt5sql5-mysql failing was reported in https://bugs.debian.org/1031863,
which includes links to more similar issues due to this change.

Libraries *must* have a stable ABI, including the version they advertise. If a
library changes behaviour in a backwards incompatible manner, even if it is to
fix a bug, it should bump the version and not just silently get shipped.

This commit fixes if for both MariaDB 10.3, 10.4 and 10.5 which all include
the MariaDB Connector C branch 3.1 at v3.1.20 (d204e83).

The 10.6 series uses branch 3.3 at v3.3.4 (12bd1d5), which had this change
*before* 10.6 was widely used, and thus users did not end up having a breaking
change in a (fully) stable release.

Thus this fix is needed only on the 3.1 branch in MariaDB Connector C.

Author: ottok

libmariadb/mariadb_lib.c

@@ -3885,7 +3885,7 @@ int STDCALL mysql_set_server_option(MYSQL *mysql,
 
 ulong STDCALL mysql_get_client_version(void)
 {
-  return MARIADB_PACKAGE_VERSION_ID;
+  return MARIADB_VERSION_ID;
 }
 
 ulong STDCALL mysql_hex_string(char *to, const char *from, unsigned long len)