Fix CI workflow - set DOCKER_IMAGE and TIDB_VERSION as env vars

Set DOCKER_IMAGE and TIDB_VERSION as environment variables in the step,
then unset the one that's not needed for each test type.
This ensures environment variables are properly available to TestMain.

Author: zph

.github/workflows/main.yml

@@ -186,22 +186,29 @@ jobs:
           GOFLAGS: -mod=vendor
           TF_ACC: 1
           GOTOOLCHAIN: auto
+          DOCKER_IMAGE: ${{ matrix.docker_image }}
+          TIDB_VERSION: ${{ matrix.db_version }}
         run: |
           export PATH="${{ github.workspace }}/bin:$PATH"
           if [ "${{ matrix.db_type }}" == "tidb" ]; then
-            export TIDB_VERSION=${{ matrix.db_version }}
+            # TiDB tests - validate TIDB_VERSION is set
             if [ -z "$TIDB_VERSION" ]; then
               echo "ERROR: TIDB_VERSION is not set for TiDB test"
               exit 1
             fi
+            # Ensure DOCKER_IMAGE is not set for TiDB tests
+            unset DOCKER_IMAGE
+            echo "Running TiDB tests with version: $TIDB_VERSION"
             go test -tags=testcontainers -v ./mysql/... -run WithTestcontainers -timeout=30m
           else
-            export DOCKER_IMAGE=${{ matrix.docker_image }}
+            # MySQL/Percona/MariaDB tests - validate DOCKER_IMAGE is set
             if [ -z "$DOCKER_IMAGE" ]; then
               echo "ERROR: DOCKER_IMAGE is not set for ${{ matrix.db_type }} test"
               exit 1
             fi
-            echo "Using Docker image: $DOCKER_IMAGE"
+            # Ensure TIDB_VERSION is not set for MySQL tests
+            unset TIDB_VERSION
+            echo "Running ${{ matrix.db_type }} tests with Docker image: $DOCKER_IMAGE"
             go test -tags=testcontainers -v ./mysql/... -run WithTestcontainers -timeout=30m
           fi
   release: