Make MySQL conditional check more Windows compatible

The bash if/else won't work in PowerShell.

Follow-up to #209

Author: swissspidy

.github/workflows/reusable-testing.yml

@@ -540,20 +540,15 @@ jobs:
           # Bust the cache at least once a month - output format: YYYY-MM.
           custom-cache-suffix: $(date -u "+%Y-%m")
 
+      # MySQL 8.4 requires explicit loading of mysql_native_password plugin
       - name: Determine MySQL authentication configuration
         id: mysql-config
-        if: ${{ matrix.dbtype != 'sqlite' }}
+        if: ${{ matrix.dbtype != 'sqlite' && matrix.mysql == 'mysql-8.4' }}
         run: |
-          if [[ "${{ matrix.mysql }}" == *"mysql-8.4"* ]]; then
-            # MySQL 8.4 requires explicit loading of mysql_native_password plugin
-            echo "auth-config<<EOF" >> $GITHUB_OUTPUT
-            echo "mysql_native_password=ON" >> $GITHUB_OUTPUT
-            echo "authentication_policy=mysql_native_password," >> $GITHUB_OUTPUT
-            echo "EOF" >> $GITHUB_OUTPUT
-          else
-            # MySQL 5.6, 5.7, 8.0 and MariaDB use the legacy configuration
-            echo "auth-config=default_authentication_plugin=mysql_native_password" >> $GITHUB_OUTPUT
-          fi
+          echo "auth-config<<EOF" >> $GITHUB_OUTPUT
+          echo "mysql_native_password=ON" >> $GITHUB_OUTPUT
+          echo "authentication_policy=mysql_native_password," >> $GITHUB_OUTPUT
+          echo "EOF" >> $GITHUB_OUTPUT
 
       - name: Setup MySQL Server
         id: setup-mysql
@@ -565,8 +560,9 @@ jobs:
           root-password: ${{ env.WP_CLI_TEST_DBROOTPASS }}
           user: ${{ env.WP_CLI_TEST_DBUSER}}
           password: ${{ env.WP_CLI_TEST_DBPASS}}
+          # Fall back to legacy configuration for MySQL 5.6, 5.7, 8.0 and MariaDB.
           my-cnf: |
-            ${{ steps.mysql-config.outputs.auth-config }}
+            ${{ steps.mysql-config.outputs.auth-config || 'default_authentication_plugin=mysql_native_password' }}
 
       - name: Prepare test database
         if: ${{ matrix.dbtype != 'sqlite' }}