fix(mysql): catch PyMySQL OperationalError exception (#7919)

## Description of changes

When trying to connect to a mySQL backend, the following error can
appear:

```
OperationalError: (pymysql.err.OperationalError) (1298, "Unknown or incorrect time zone: 'UTC'")
(Background on this error at: https://sqlalche.me/e/20/e3q8)
```

This is due to an exception generated by PyMySQL.
The exception, formerly generated by SQLAlchemy was already caught by
Ibis since #6010, this PR adds a catching of the PyMySQL exception.

## Issues closed
Resolves #7918

ibis/backends/mysql/__init__.py

@@ -5,6 +5,7 @@
 import warnings
 from typing import TYPE_CHECKING, Literal
 
+import pymysql
 import sqlalchemy as sa
 from sqlalchemy.dialects import mysql
 
@@ -112,7 +113,7 @@ def connect(dbapi_connection, connection_record):
             with dbapi_connection.cursor() as cur:
                 try:
                     cur.execute("SET @@session.time_zone = 'UTC'")
-                except sa.exc.OperationalError:
+                except (sa.exc.OperationalError, pymysql.err.OperationalError):
                     warnings.warn("Unable to set session timezone to UTC.")
 
         super().do_connect(engine)