Hold Dependabot updates for 14 days to match the resolver shield

pyproject.toml sets uv's exclude-newer to 14 days, so a floor raised to a
release younger than that resolves to nothing and every CI job dies in the
install step. PR #48 raised tox to >=4.61.4 and hit exactly that: only
tox<=4.61.2 was visible to the resolver. A 14 day cooldown lines the two up,
the way portalocker and mt940 already do.

Author: wolph

.github/dependabot.yml

@@ -5,6 +5,8 @@ updates:
     target-branch: develop
     schedule:
       interval: weekly
+    cooldown:
+      default-days: 14
     groups:
       actions:
         patterns: ['*']
@@ -14,6 +16,8 @@ updates:
     target-branch: develop
     schedule:
       interval: weekly
+    cooldown:
+      default-days: 14
     groups:
       python-dev-dependencies:
         patterns: ['*']