Add support go 1.21.x / drop 1.16.x (#282)

* Update ci.yml

* Update dependabot.yml

Author: nukosuke

.github/dependabot.yml

@@ -10,3 +10,12 @@ updates:
     schedule:
       interval: "weekly"
       day: "saturday"
+      time: "10:00"
+      timezone: "Asia/Tokyo"
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+      day: "saturday"
+      time: "10:00"
+      timezone: "Asia/Tokyo"

.github/workflows/ci.yml

@@ -7,11 +7,11 @@ jobs:
     strategy:
       matrix:
         go-version:
-          - 1.16.x
           - 1.17.x
           - 1.18.x
           - 1.19.x
           - 1.20.x
+          - 1.21.x
     runs-on: ubuntu-latest
     steps:
     - name: Set up Go 1.x