Completer TestExec re #5782

Signed-off-by: Karl Palmen <karl.palmen@stfc.ac.uk>
Add test for exception if base instruments are different re #5782

Also in previous test, verified to two workspaces do have different instruments,
even though the base instrument is the same.

Signed-off-by: Karl Palmen <karl.palmen@stfc.ac.uk>
Merge branch 'feature/5782_copy_inst_param_test' into develop