libcaption: Fix header missing in install

libobs directly depends on libcaption headers. So ensure they are
installed with obs' headers.

fixes #3925

deps/libcaption/CMakeLists.txt

@@ -36,6 +36,7 @@ set(CAPTION_HEADERS
 )
 
 add_library(caption STATIC ${CAPTION_SOURCES})
+install_obs_headers("caption/caption.h")
 set_target_properties(caption PROPERTIES
 	FOLDER "deps"
 	POSITION_INDEPENDENT_CODE ON)