Fix output.safe_write() in connection with NamedTemporaryFile

Fixes: AttributeError: '_io.BufferedRandom' object has no attribute 'buffer'

tests/test_output.py

@@ -1,10 +1,12 @@
 import contextlib
 import io
+import tempfile
 import unittest
 
 import osc.conf
 from osc.output import KeyValueTable
 from osc.output import print_msg
+from osc.output import safe_write
 from osc.output import sanitize_text
 from osc.output import tty
 
@@ -238,5 +240,23 @@ class TestSanitization(unittest.TestCase):
         self.assertEqual(sanitized, b"0;this is the window title")
 
 
+class TestSafeWrite(unittest.TestCase):
+    def test_string_to_file(self):
+        with tempfile.NamedTemporaryFile(mode="w+") as f:
+            safe_write(f, "string")
+
+    def test_bytes_to_file(self):
+        with tempfile.NamedTemporaryFile(mode="wb+") as f:
+            safe_write(f, b"bytes")
+
+    def test_string_to_stringio(self):
+        with io.StringIO() as f:
+            safe_write(f, "string")
+
+    def test_bytes_to_bytesio(self):
+        with io.BytesIO() as f:
+            safe_write(f, b"bytes")
+
+
 if __name__ == "__main__":
     unittest.main()