Install compressionstream private header

CMakeLists.txt

 cmake_minimum_required(VERSION 3.5)
 
-set(PIM_VERSION "5.15.90")
+set(PIM_VERSION "5.15.91")
 project(Akonadi VERSION ${PIM_VERSION})
 
 set(CMAKE_CXX_STANDARD 17)

src/private/CMakeLists.txt

@@ -104,6 +104,7 @@ install(FILES
     capabilities_p.h
     scope_p.h
     tristate_p.h
+    compressionstream_p.h
     DESTINATION ${KF5_INCLUDE_INSTALL_DIR}/akonadi/private
 )