Reduce Dependabot toil; configure cooldowns (#1367)

Author: kurtmckee

.github/dependabot.yml .github/dependabot.yaml.github/dependabot.yml renamed to .github/dependabot.yaml

@@ -3,7 +3,9 @@ updates:
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule:
-      interval: "monthly"
+      interval: "semiannually"
+    cooldown:
+      default-days: 20
     groups:
       github-actions:
         patterns:
@@ -13,6 +15,6 @@ updates:
   - package-ecosystem: "pip"
     directory: "/requirements/"
     schedule:
-      interval: "monthly"
+      interval: "semiannually"
     ignore:
       - dependency-name: "*"