build/tests: Check for python found and version in single require call

We can only use the python object if it was found and the arguments for
require are all evaluated, even if the resulting feature is disabled.

Fixes: 1c6dd18 ("tests: Check for required WAV decoder for notification tests")
Closes: flatpak#1547

tests/meson.build

@@ -284,8 +284,7 @@ python = pymod.find_installation(
 
 enable_pytest = get_option('pytest') \
   .require(pytest.found()) \
-  .require(python.found()) \
-  .require(python.language_version().version_compare('>=3.9'),
+  .require(python.found() and python.language_version().version_compare('>=3.9'),
            error_message: 'Python version >=3.9 is required') \
   .require(umockdev_dep.found()) \
   .require(have_wav_parse,