Updates geometry hash

Changes the default MVD geometry from "v20c_tr" to "v20a_tr" in the hadron and electron setup files to be compatible with STS "v19a". This is documented in https://redmine.cbm.gsi.de/issues/2119 and discussed in SWM on 2021-05-20 and 2021-05-27.

external/InstallGeometry.cmake

-set(GEOMETRY_VERSION fec96a5edc68763373d81c5eb2b1ff9dcf3d4208)
+set(GEOMETRY_VERSION bb048703d1e76dfbfe6c4dfbba2a5d2f0a6279a6)
 
 set(GEOMETRY_SRC_URL "https://git.cbm.gsi.de/CbmSoft/cbmroot_geometry.git")