add Go 1.21 and MySQL 8.1 to the build matrix (#1472)

* add Go 1.21 and MySQL 8.1 to the build matrix

* bump shogo82148/actions-setup-mysql v1.21.0

Author: shogo82148

.github/workflows/test.yml

@@ -31,12 +31,14 @@ jobs:
           import os
           go = [
               # Keep the most recent production release at the top
-              '1.20',
+              '1.21',
               # Older production releases
+              '1.20',
               '1.19',
               '1.18',
           ]
           mysql = [
+              '8.1',
               '8.0',
               '5.7',
               '5.6',
@@ -75,7 +77,7 @@ jobs:
       - uses: actions/setup-go@v4
         with:
           go-version: ${{ matrix.go }}
-      - uses: shogo82148/actions-setup-mysql@v1.16.0
+      - uses: shogo82148/actions-setup-mysql@v1.21.0
         with:
           mysql-version: ${{ matrix.mysql }}
           user: ${{ env.MYSQL_TEST_USER }}