Add C# artifacts to `.gitignore` for `multi-language-repo` #7641

Job	Run time
Packaging: Config file (ubuntu-latest, linked)	1m 56s
Packaging: Config file (windows-latest, linked)	6m 5s
Packaging: Config file (macos-latest, nightly-latest)	2m 1s
Packaging: Config file (ubuntu-latest, default)	3m 5s
Packaging: Config file (ubuntu-latest, nightly-latest)	1m 55s
Packaging: Config file (windows-latest, nightly-latest)	5m 49s
Packaging: Config file (windows-latest, default)	6m 47s
Packaging: Config file (macos-latest, default)	2m 5s
Packaging: Config file (macos-latest, linked)	2m 0s
	31m 43s

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