Add support of pre-release Python versions (#112)

* Add support of unstable Python versions

* Update README

* Get rid of stable boolean input

* Fix typo in the test.yml

* Update README

Co-authored-by: MaksimZhukov <v-mazhuk@microsoft.com>

src/install-python.ts

@@ -26,7 +26,7 @@ export async function findReleaseFromManifest(
   );
   return await tc.findFromManifest(
     semanticVersionSpec,
-    true,
+    false,
     manifest,
     architecture
   );