Fake a dependabot increase-if-necessary strategy

At the moment, the cargo ecosystem does not support the strategy
directly, so I'm going to see if dependabot will allow multiple
definitions for the same ecosystem in order to work around the problem.

See:
- https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file#versioning-strategy
- dependabot/dependabot-core#4009

Author: elasticdog

.github/dependabot.yml

@@ -5,6 +5,17 @@ updates:
     directory: /
     schedule:
       interval: weekly
+    versioning-strategy: lockfile-only
+
+  - package-ecosystem: cargo
+    directory: /
+    schedule:
+      interval: weekly
+    ignore:
+      - dependency-name: "*"
+        update-types:
+          - version-update:semver-patch
+          - version-update:semver-minor
 
   - package-ecosystem: github-actions
     directory: /