Make sure to close file stream after backup upload (home-assistant#5723)

* Make sure to close file stream after backup upload

Currently the file stream does not get closed before importing the file
stream. It seems the test case didn't catch that, presumably because
it is a race condition if the bytes get flushed to disk or not.

Properly close the stream before continue handling the file.

* Close file stream in executor

* Add comment about closing twice is fine

Author: agners

supervisor/api/backups.py

@@ -531,6 +531,8 @@ def open_backup_file() -> Path:
 
         def close_backup_file() -> None:
             if backup_file_stream:
+                # Make sure it got closed, in case of exception. It is safe to
+                # close the file stream twice.
                 backup_file_stream.close()
             if temp_dir:
                 temp_dir.cleanup()
@@ -541,6 +543,7 @@ def close_backup_file() -> None:
             tar_file = await self.sys_run_in_executor(open_backup_file)
             while chunk := await contents.read_chunk(size=2**16):
                 await self.sys_run_in_executor(backup_file_stream.write, chunk)
+            await self.sys_run_in_executor(backup_file_stream.close)
 
             backup = await asyncio.shield(
                 self.sys_backups.import_backup(
@@ -563,8 +566,7 @@ def close_backup_file() -> None:
             return False
 
         finally:
-            if temp_dir or backup:
-                await self.sys_run_in_executor(close_backup_file)
+            await self.sys_run_in_executor(close_backup_file)
 
         if backup:
             return {ATTR_SLUG: backup.slug}