Update oidc-exchange.py

Co-authored-by: Christian Clauss <[email protected]>

Author: woodruffw

oidc-exchange.py

@@ -27,7 +27,7 @@
 
 
 def die(msg: str) -> NoReturn:
-    with _GITHUB_STEP_SUMMARY.open("a") as io:
+    with _GITHUB_STEP_SUMMARY.open("a", encoding="utf-8") as io:
         print(msg, file=io)
 
     # NOTE: `msg` is Markdown formatted, so we emit only the header line to