Set Dependabot cooldown to 3 days (#3228)

Enforces the central supply-chain cooldown on `.github/dependabot.yml`
(`cooldown.default-days = 3`) on every `updates:` entry.

New dependency versions are held for this many days before Dependabot
proposes a version update, so a compromised release has time to be
detected. Security updates (published GHSA/CVE advisories) bypass the
cooldown and are unaffected.

Opened by the central
[`dependabot-cooldown`](https://github.com/softwaremill/github-actions-workflows/blob/main/.github/workflows/dependabot-cooldown.yml)
workflow.

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: sml-dependabot-cooldown[bot]

.github/dependabot.yml

@@ -10,3 +10,5 @@ updates:
     allow:
       - dependency-type: "direct"
       - dependency-type: "indirect"
+    cooldown:
+      default-days: 3