[code]: Update marketplace.json

[filiptronicek]

Description

Update to reflect the latest changes done by Microsoft (only updating those that are interesting to us)

--- a/marketplace.json
+++ b/marketplace.json
@@ -382,6 +382,13 @@
 				"displayName": "Vue Language Features (Volar)"
 			}
 		},
+		"silvenon.mdx": {
+			"disallowInstall": true,
+			"extension": {
+				"id": "unifiedjs.vscode-mdx",
+				"displayName": "VSCode MDX"
+			}
+		},
 		"CoenraadS.bracket-pair-colorizer-2": {
 			"settings": [
 				"editor.bracketPairColorization.enabled",

How to test

You can test by searching for silvenon.mdx in the extensions in VS Code Browser and confirming it cannot be downloaded.

Release Notes

NONE

Werft options:

• /werft with-preview