umu_runtime: fix steamrt always updating each launch

- In the case the runtime gets updated, differences in character encoding of the VERSIONS.txt files may cause the launcher to always update on subsequent launches. Another http client library will be explored in the future to handle future redirects for Github and Cloudflare, and for more robust handling of networking errors.

- Related to #188

umu/umu_runtime.py

@@ -332,7 +332,10 @@ def _update_umu(
         )
         return
 
-    steamrt_latest_digest: bytes = sha256(resp.read()).digest()
+    versions_utf8: str = resp.read().decode(encoding="utf-8")
+    steamrt_latest_digest: bytes = sha256(
+        versions_utf8.encode(encoding="utf-8")
+    ).digest()
 
     if (
         steamrt_latest_digest