chore: speed up lint job

.github/workflows/ci.yaml

@@ -68,6 +68,8 @@ jobs:
       id: date
       run: echo "::set-output name=week_of_year::$(date +'%W' --utc)"
     - uses: actions/checkout@v4
+      with:
+        fetch-depth: 0
     - uses: actions/setup-java@v4
       with:
         distribution: temurin
@@ -79,8 +81,11 @@ jobs:
         path: ~/.m2/repository
         key: ${{ runner.os }}-maven-unified-${{ steps.date.outputs.week_of_year }}
     - run: java -version
-    - run: mvn -B -ntp com.spotify.fmt:fmt-maven-plugin:check -T 1C
-    - run: mvn -B -ntp checkstyle:check@checkstyle
+    - run: .kokoro/build.sh
+      env:
+        JOB_TYPE: lint
+        HEAD_BRANCH: ${{ github.head_ref }}
+        BASE_BRANCH: ${{ github.base_ref }}
   enforcer:
     runs-on: ubuntu-latest
     steps:

.kokoro/build.sh

@@ -92,6 +92,27 @@ case ${JOB_TYPE} in
       echo "Not running GraalVM checks -- No changes in relevant modules"
     fi
     ;;
+  lint)
+    git checkout "${BASE_BRANCH}"
+    git checkout "${HEAD_BRANCH}"
+    changed_file_list="$(git diff --name-only "${BASE_BRANCH}" HEAD)"
+    has_code_change="false"
+    while IFS= read -r changed_file; do
+        if [ -n "${changed_file}" ] && [[ "${changed_file}" == *.java ]]; then
+            has_code_change="true"
+            break
+        fi
+    done <<< "${changed_file_list}"
+    if [ "${has_code_change}" == "false" ]; then
+        echo "No java modules affected. Skipping linter check."
+        exit 0
+    fi
+
+    mvn -B -ntp \
+      -T 1.5C \
+      com.spotify.fmt:fmt-maven-plugin:check
+    mvn -B -ntp checkstyle:check@checkstyle
+    ;;
   *) ;;
 
 esac