Update Go testing

* Update minimum supported Go version to 1.23.0.
* Bump GitHub actions and pin versions for supply chain security.
* Enable dependabot to update GitHub actions.

Signed-off-by: SuperQ <superq@gmail.com>

Author: SuperQ

.github/dependabot.yml

@@ -0,0 +1,6 @@
+version: 2
+updates:
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: monthly

.github/workflows/test.yml

@@ -9,16 +9,18 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        go-version: [ '1.18', '1.21' ]
+        go-version:
+          - '1.23.x'
+          - '1.24.x'
 
     steps:
       - name: install memcached
         run: |
           sudo apt update
           sudo apt install memcached
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683  # v4.2.2
       - name: Setup Go ${{ matrix.go-version }}
-        uses: actions/setup-go@v4
+        uses: actions/setup-go@0aaccfd150d50ccaeb58ebd88d36e91967a5f35b  # v5.4.0
         with:
           go-version: ${{ matrix.go-version }}
       - name: Test

go.mod

@@ -1,3 +1,3 @@
 module github.com/bradfitz/gomemcache
 
-go 1.18
+go 1.23.0