chore(java): update windows build (#1205)

to install maven 3.8.1 at runtime too (related to #1202)

Tested in [java-bigquerystorage](googleapis/java-bigquerystorage@7834f4f)

synthtool/gcp/templates/java_library/.github/workflows/ci.yaml

@@ -26,6 +26,9 @@ jobs:
     runs-on: windows-latest
     steps:
     - uses: actions/checkout@v2
+    - uses: stCarolas/setup-maven@v4
+      with:
+        maven-version: 3.8.1
     - uses: actions/setup-java@v1
       with:
         java-version: 8
@@ -75,4 +78,4 @@ jobs:
     - run: java -version
     - run: .kokoro/build.sh
       env:
-        JOB_TYPE: clirr
+        JOB_TYPE: clirr