[FLINK-38722] Upgrade HBase to 2.6.4

[mateczagany]

• Bump Flink version to 1.20.3
• HBase 2.6.3 no longer exists here since the release of 2.6.4: https://dlcdn.apache.org/hbase/
• Had to exclude HBaseJupiterExtension as it caused all tests to fail because some HBase-specific annotations were not present. This extension is used only in the HBase repo that adds timeout to the tests based on annotations, so it's probably safer to disable it altogether.
• JUnit had to be upgraded because junit.jupiter.extensions.autodetection.exclude is only available since JUnit 5.12.x