Merge pull request #7252 from puetzk/test_size_on_disk_accurate-flush-1.2

[1.2-maint] Fix test_size_on_disk_accurate for large st_blksize, fixes #7250

src/borg/testsuite/hashindex.py

@@ -196,9 +196,9 @@ class HashIndexSizeTestCase(BaseTestCase):
         idx = ChunkIndex()
         for i in range(1234):
             idx[H(i)] = i, i**2, i**3
-        with tempfile.NamedTemporaryFile() as file:
-            idx.write(file)
-            size = os.path.getsize(file.fileno())
+        with unopened_tempfile() as filepath:
+            idx.write(filepath)
+            size = os.path.getsize(filepath)
         assert idx.size() == size