Concurrent modification of session stored in hsqldb can result in HsqlException: integrity constraint violation: unique constraint or index violation ; SPRING_SESSION_ATTRIBUTES_PK table: SPRING_SESSION_ATTRIBUTES

Describe the bug
Running a spring-boot web application using spring-session-jdbc: when spring-session-jdbc is configured to store the session in an hsql database, if two concurrent http requests are handled from the same user, and attempt to insert the same attribute into the session, they can fail with the following exception message:

HsqlException: integrity constraint violation: unique constraint or index violation ; SPRING_SESSION_ATTRIBUTES_PK table: SPRING_SESSION_ATTRIBUTES

To Reproduce
See Describe the bug

Expected behavior
Session attributes are inserted or updated similar to how they would be with an in-memory session; or if using another relational database which already has upsert query configured for session attribute, e.g. postgres and using PostgreSqlJdbcIndexedSessionRepositoryCustomizer

Sample
In progress.

Start by reproducing concurrent requests against a Spring Session JDBC store using HSQLDB, as described in the issue. Compare the session-attribute insert behavior with the PostgreSQL upsert configuration; done means concurrent requests updating the same attribute no longer produce a unique-constraint violation.