Run Dependabot independently on each branch

Author: hugovk

.github/dependabot.yml

@@ -16,6 +16,101 @@ updates:
       # Cooldowns protect against supply chain attacks by avoiding the
       # highest-risk window immediately after new releases.
       default-days: 14
+
+  # Release branches: Dependabot only reads this file from the default
+  # branch, so each branch that should get its own actions bumps needs an
+  # entry here with `target-branch`. Add one when a new release branch is
+  # created, and remove when the branch reaches end-of-life.
+  - package-ecosystem: "github-actions"
+    target-branch: "3.15"
+    directory: "/"
+    schedule:
+      interval: "quarterly"
+    labels:
+      - "skip issue"
+      - "skip news"
+    groups:
+      actions:
+        patterns:
+          - "*"
+    cooldown:
+      default-days: 14
+
+  - package-ecosystem: "github-actions"
+    target-branch: "3.14"
+    directory: "/"
+    schedule:
+      interval: "quarterly"
+    labels:
+      - "skip issue"
+      - "skip news"
+    groups:
+      actions:
+        patterns:
+          - "*"
+    cooldown:
+      default-days: 14
+
+  - package-ecosystem: "github-actions"
+    target-branch: "3.13"
+    directory: "/"
+    schedule:
+      interval: "quarterly"
+    labels:
+      - "skip issue"
+      - "skip news"
+    groups:
+      actions:
+        patterns:
+          - "*"
+    cooldown:
+      default-days: 14
+
+  - package-ecosystem: "github-actions"
+    target-branch: "3.12"
+    directory: "/"
+    schedule:
+      interval: "quarterly"
+    labels:
+      - "skip issue"
+      - "skip news"
+    groups:
+      actions:
+        patterns:
+          - "*"
+    cooldown:
+      default-days: 14
+
+  - package-ecosystem: "github-actions"
+    target-branch: "3.11"
+    directory: "/"
+    schedule:
+      interval: "quarterly"
+    labels:
+      - "skip issue"
+      - "skip news"
+    groups:
+      actions:
+        patterns:
+          - "*"
+    cooldown:
+      default-days: 14
+
+  - package-ecosystem: "github-actions"
+    target-branch: "3.10"
+    directory: "/"
+    schedule:
+      interval: "quarterly"
+    labels:
+      - "skip issue"
+      - "skip news"
+    groups:
+      actions:
+        patterns:
+          - "*"
+    cooldown:
+      default-days: 14
+
   - package-ecosystem: "pip"
     directory: "/Tools/"
     schedule: