Group dependabot updates.

Also use dependabot to update github actions.

.github/dependabot.yml

@@ -1,9 +1,50 @@
 version: 2
 updates:
-- package-ecosystem: pip
+- package-ecosystem: "github-actions"
   directory: "/"
+  target-branch: main
   schedule:
-    interval: monthly
-  open-pull-requests-limit: 10
+    interval: "monthly"
+    time: "07:00"
+    timezone: "EST5EDT"
+  pull-request-branch-name:
+    separator: "-"
+  open-pull-requests-limit: 2
   reviewers:
-    - glotzerlab/signac-maintainers
+  - joaander
+  groups:
+    actions-version:
+      applies-to: version-updates
+      patterns:
+      - '*'
+    actions-security:
+      applies-to: security-updates
+      patterns:
+      - '*'
+- package-ecosystem: "pip"
+  directory: "/"
+  target-branch: main
+  schedule:
+    interval: "monthly"
+    time: "07:00"
+    timezone: "EST5EDT"
+  pull-request-branch-name:
+    separator: "-"
+  open-pull-requests-limit: 2
+  reviewers:
+  - joaander
+  groups:
+    pip-version:
+      applies-to: version-updates
+      patterns:
+      - '*'
+      update-types:
+      - minor
+      - patch
+    pip-security:
+      applies-to: security-updates
+      patterns:
+      - '*'
+      update-types:
+      - minor
+      - patch