CMake: bump absl: master -> 8ba96a8
CMake: bump absl: master -> 8ba96a8

be consistent with Makefile, don't follow a moving target (i.e. don't live at head)

or-tools/or-tools,or-tools/or-tools,or-tools/or-tools,or-tools/or-tools,google/or-tools,google/or-tools,google/or-tools,or-tools/or-tools,google/or-tools,google/or-tools,google/or-tools,or-tools/or-tools