tools/sincechecker/modules/java.base/JavaBaseCheckSince.java fails with the start of release updates for JDK 26.

The since checker needs to be updated to handle JDK 26.
The symbol information in the early access builds of OpenJDK often lags behind the actual API changes.
For example if an API was added on day J, but the build and symbol information are from day J-1, the checker flags the new APIs as being from the release N+1.

To address this, we should temporarily disable the test, and then we can remove it from the problem list once the symbol information is up to date.