Update Dependabot doc

Author: AArnott

docfx/docs/shallow-cloning-agents.md

@@ -27,4 +27,9 @@ See also [GitHub Copilot Coding Agent docs](https://docs.github.com/en/copilot/h
 
 ## Dependabot
 
-We don't anticipate any issues with Dependabot, which [now sets](https://github.com/dependabot/dependabot-core/issues/4660#issuecomment-3181471227) `NBGV_GitEngine=Disabled` automatically.
+Dependabot does not yet allow configuring custom environment variables for its runtime environment.
+Consider up-voting [this issue](https://github.com/dependabot/dependabot-core/issues/4660).
+Be sure to vote up the top-level issue description as that tends to be the tally that maintainers pay attention to.
+But you may also upvote [this particular comment](https://github.com/dependabot/dependabot-core/issues/4660#issuecomment-3170935213) that describes our use case.
+
+There is [a known workaround](https://github.com/dependabot/dependabot-core/issues/4660#issuecomment-3399907801) for the time being.