ci: Update ggshield to v1.46.0 and add Dependabot for pre-commit

- Update ggshield from v1.35.0 to v1.46.0 for latest security detectors
- Add pip ecosystem to Dependabot to auto-update pre-commit hooks

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: tablackburn

.github/dependabot.yml

@@ -9,3 +9,13 @@ updates:
     labels:
       - "dependencies"
       - "github-actions"
+
+  - package-ecosystem: "pip"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    commit-message:
+      prefix: "ci"
+    labels:
+      - "dependencies"
+      - "pre-commit"

.pre-commit-config.yaml

@@ -1,6 +1,6 @@
 repos:
   - repo: https://github.com/gitguardian/ggshield
-    rev: v1.35.0
+    rev: v1.46.0
     hooks:
       - id: ggshield
         language_version: python3