Repo File Sync: Update DocBuild File is not always closed

[odaysec]

Fix issue problem the file opens in MakeYml should be wrapped in with context managers so they are always closed, even if an exception occurs. We still need to preserve current behavior: copy all lines from the base YAML file into the output file, then parse the base YAML from the beginning to check for an extra key, raise if present, and finally keep an open handle to the output YAML in self.Yml for later use by CloseYml.

The safest change is:

• Open self.YmlFilePathBase with with open(..., 'r') as ymlbase: so that it is always closed after use.
• Within that with, open self.YmlFilePathOut with another with open(..., 'w') as yamlout: and perform the line copy and YAML parse while both files are open and automatically managed.
• After the nested with blocks, reopen self.YmlFilePathOut in append mode ('a') and assign that handle to self.Yml. This preserves the design where self.Yml stays open beyond MakeYml and will be closed in CloseYml, without risking leaks if an exception occurs during the initial processing.
• Remove the explicit ymlbase.close() and the assignment self.Yml = yamlout inside MakeYml, since those handles are now managed by context managers and a fresh handle is created for self.Yml.

Reading and writing files
The with statement, The try statement
Python PEP 343 The "with" Statement
CWE-772