python3: Fix tests on Windows as it uses 'Lib' and 'Include'

test cases/python3/1 basic/meson.build

@@ -9,18 +9,19 @@ if py3_version.version_compare('< 3.2')
 endif
 
 py3_purelib = py3_mod.sysconfig_path('purelib')
-if not py3_purelib.startswith('lib') or not py3_purelib.endswith('site-packages')
+if not py3_purelib.to_lower().startswith('lib') or not py3_purelib.endswith('site-packages')
   error('Python3 purelib path seems invalid?')
 endif
 
-# could be 'lib64' on some systems
+# could be 'lib64' or 'Lib' on some systems
 py3_platlib = py3_mod.sysconfig_path('platlib')
-if not py3_platlib.startswith('lib') or not py3_platlib.endswith('site-packages')
+if not py3_platlib.to_lower().startswith('lib') or not py3_platlib.endswith('site-packages')
   error('Python3 platlib path seems invalid?')
 endif
 
+# could be 'Include' on Windows
 py3_include = py3_mod.sysconfig_path('include')
-if not py3_include.startswith('include')
+if not py3_include.to_lower().startswith('include')
   error('Python3 include path seems invalid?')
 endif