fix(keycloak): Fixed Keycloak testcontainer for latest version v26.1.0 (#766)

@alexanderankin We already discussed last year that we only want to
support the latest Keycloak version.

I added the `latest` tag to test parameterization so we get a better
feedback for future Keycloak updates.

Fixes https://github.com/testcontainers/testcontainers-python/issues/764

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Co-authored-by: David Ankin <daveankin@gmail.com>