Group boost vcpkg ports in Dependabot (#1359)

Dependabot updates each port _individually_ which is annoying:
- #1355
- #1356
- #1357

Instead, [configure Dependabot to group
them](https://docs.github.com/en/code-security/dependabot/working-with-dependabot/dependabot-options-reference#groups--).
It would be preferable to remove the version specification in the
`vcpkg` file itself, but this isn't possible.

I'm not able to (easily) test this change until it's merged.

Author: JackPGreen

.github/dependabot.yml

@@ -4,6 +4,10 @@ updates:
     directory: "/"
     schedule:
       interval: "weekly"
+    groups:
+      boost:
+        patterns:
+          - "boost-*"
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule: