build: don't install include/BUILD.bazel (#1107)

CMakeLists.txt

@@ -282,7 +282,13 @@ install(
     DESTINATION ${CMAKE_INSTALL_LIBDIR}/EnTT/cmake
 )
 
-install(DIRECTORY src/ DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
+install(
+    DIRECTORY src/
+    DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
+    FILES_MATCHING
+    PATTERN "*.h"
+    PATTERN "*.hpp"
+)
 
 export(PACKAGE EnTT)