fix: append to GITHUB_OUTPUT

Author: mrsobakin

gha-helper/gha_helper/gh.py

@@ -58,12 +58,12 @@ def get_json(self, name: str, default=Unset):
 
 class Output:
     def save(self, name: str, value: Any):
-        with open(os.environ["GITHUB_OUTPUT"], "w+") as f:
+        with open(os.environ["GITHUB_OUTPUT"], "a") as f:
             f.write(f"{name}={value}\n")
 
     def save_json(self, name: str, value: Any):
         data = json.dumps(value, separators=(",", ":"))
-        with open(os.environ["GITHUB_OUTPUT"], "w+") as f:
+        with open(os.environ["GITHUB_OUTPUT"], "a") as f:
             f.write(f"{name}={data}\n")