[pstl] Do not install the __config_site.in file

The generated version of the file is already installed -- we shouldn't
install the pre-generation version of the file.

GitOrigin-RevId: ef14e52be4e1ce4a6aa2a28738aed2cfcc0a31f1
diff --git a/CMakeLists.txt b/CMakeLists.txt
index dd601bc..8e6e135 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -86,7 +86,8 @@
               "${CMAKE_CURRENT_BINARY_DIR}/ParallelSTLConfigVersion.cmake"
         DESTINATION lib/cmake/ParallelSTL)
 install(DIRECTORY include/
-        DESTINATION include)
+        DESTINATION include
+        PATTERN "*.in" EXCLUDE)
 install(FILES "${PSTL_CONFIG_SITE_PATH}"
         DESTINATION include)