cmake: rename git2internal target to libgit2

The `git2internal` target is actually the git library; call it such so
that IDE users have visibility into it.

examples/CMakeLists.txt

@@ -12,7 +12,7 @@ target_include_directories(lg2 PRIVATE ${LIBGIT2_INCLUDES} ${LIBGIT2_DEPENDENCY_
 target_include_directories(lg2 SYSTEM PRIVATE ${LIBGIT2_SYSTEM_INCLUDES})
 
 if(WIN32 OR ANDROID)
-	target_link_libraries(lg2 git2)
+	target_link_libraries(lg2 libgit2package)
 else()
-	target_link_libraries(lg2 git2 pthread)
+	target_link_libraries(lg2 libgit2package pthread)
 endif()