Rename testGetByIndex to testIndex of sheet::XSheetAnnotations test
cases so it won't collide with testGetByIndex of
container::XIndexAccess.

Change-Id: Ic48ffe954c9f4f00b68066ad5d0d2df89cc4dfd7
Reviewed-on: https://gerrit.libreoffice.org/64402
Tested-by: Jenkins
Reviewed-by: Jens Carl <j.carl43@gmx.de>