Group dependabot updates.

.github/dependabot.yml

@@ -1,23 +1,50 @@
 version: 2
 updates:
-- package-ecosystem: pip
+- package-ecosystem: "github-actions"
   directory: "/"
+  target-branch: main
   schedule:
-    interval: "weekly"
+    interval: "monthly"
     time: "07:00"
     timezone: "EST5EDT"
+  pull-request-branch-name:
+    separator: "-"
   open-pull-requests-limit: 2
   reviewers:
-    - glotzerlab/signac-maintainers
-- package-ecosystem: "github-actions"
+  - 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: "weekly"
+    interval: "monthly"
     time: "07:00"
     timezone: "EST5EDT"
   pull-request-branch-name:
     separator: "-"
-  reviewers:
-    - glotzerlab/signac-maintainers
   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