Dependabot: only update vcpkg dependencies for major releases

This detects incompatibilities with possibly breaking changes with vcpkg
dependencies. Note, however, that github actions are upgraded for every
release as they may contain security relevant fixes for the CI
workflows.

Author: frankmorgner

.github/dependabot.yml

@@ -8,6 +8,11 @@ updates:
     directory: "/.github/" # Location of vcpkg.json file
     schedule:
       interval: "weekly"
+    ignore:
+      - dependency-name: "*"
+        update-types:
+          - "version-update:semver-minor"
+          - "version-update:semver-patch"
 
   # https://docs.github.com/en/code-security/how-tos/secure-your-supply-chain/secure-your-dependencies/keeping-your-actions-up-to-date-with-dependabot
   - package-ecosystem: "github-actions"