cmake - fix python install path being treated as absolute

Otherwise it was installing binary in my case (Windows) to `Installing: /Lib/site-packages/libtorrent.cp313-win_amd64.pyd` which means `"L:\Lib\site-packages\libtorrent.cp313-win_amd64.pyd"` instead of `L:/my/install/prefix/Lib\site-packages\libtorrent.cp313-win_amd64.pyd`

Author: Andrej730

bindings/python/CMakeLists.txt

@@ -96,7 +96,8 @@ else()
 	execute_process(
 		COMMAND "${Python3_EXECUTABLE}" -c [=[
 import sysconfig
-print(sysconfig.get_path('platlib', vars={'platbase': '', 'base': ''}))
+# Strip leading separator - cmake would otherwise treat this as an absolute path.
+print(sysconfig.get_path('platlib', vars={'platbase': '', 'base': ''}).lstrip('/\\'))
 ]=]
 		OUTPUT_VARIABLE _PYTHON3_SITE_ARCH
 		OUTPUT_STRIP_TRAILING_WHITESPACE