Update extensions.json

Author: benpaddlejones

.vscode/extensions.json

@@ -8,7 +8,7 @@
     "GitHub.codespaces",
     "ms-python.debugpy",
     "ms-python.vscode-pylance",
-    "yahyabatulu.vscode-markdown-alert",
+    "saeris.markdown-github-alerts",
     "bierner.markdown-preview-github-styles",
     "mechatroner.rainbow-csv",
     "ms-python.pylint",