Avoid ClassCastException in Codan Run job

Occasionally Run Code Analysis actions get text selection
instead of structured selection so it is failing and logging
CCE. Avoid this by non accepting other selections.

Change-Id: Ia3583755547e5251a057290e506184656ebf2d5a
Signed-off-by: Alena Laskavaia <elaskavaia.cdt@gmail.com>
Reviewed-on: https://git.eclipse.org/r/37306
Reviewed-by: Sergey Prigogin <eclipse.sprigogin@gmail.com>