Cleanup: Alembic, rename unit test

This rename is to prepare for a future addition to the unit test file.
Currently it's named "import" and I will add an export test as well. The
rename is a separate commit to easily see the difference between the
rename and the addition of another test.

No functional changes.

tests/python/CMakeLists.txt

@@ -644,8 +644,8 @@ if(WITH_ALEMBIC)
   )
 
   add_blender_test(
-    script_alembic_import
-    --python ${CMAKE_CURRENT_LIST_DIR}/bl_alembic_import_test.py
+    script_alembic_io
+    --python ${CMAKE_CURRENT_LIST_DIR}/bl_alembic_io_test.py
     --
     --testdir "${TEST_SRC_DIR}/alembic"
   )

tests/python/bl_alembic_io_test.py

@@ -19,7 +19,7 @@
 # <pep8 compliant>
 
 """
-./blender.bin --background -noaudio --factory-startup --python tests/python/bl_alembic_import_test.py -- --testdir /path/to/lib/tests/alembic
+./blender.bin --background -noaudio --factory-startup --python tests/python/bl_alembic_io_test.py -- --testdir /path/to/lib/tests/alembic
 """
 
 import pathlib