Run Java tests on generated schemas in stefgen on Github

We have testcases in stefgen/generator/testdata which currently generate Go and Java code from schemas, but only run Go tests. We need to also run Java tests.

The action sets up both Go and Java, builds stefgen using Go, generates Java code from schemas using stefgen, then runs Java tests.

Author: tigrannajaryan

.github/workflows/java-schema-test.yml

@@ -0,0 +1,50 @@
+name: Java Schema Generation and Test
+
+on:
+  push:
+    paths:
+      - stefgen/generator/testdata/**
+      - stefgen/**
+      - java/**
+  pull_request:
+    paths:
+      - stefgen/generator/testdata/**
+      - stefgen/**
+      - java/**
+
+jobs:
+  generate-and-test-java:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        java-version: [17, 21]
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: '1.22'
+
+      - name: Set up JDK ${{ matrix.java-version }}
+        uses: actions/setup-java@v4
+        with:
+          distribution: 'temurin'
+          java-version: ${{ matrix.java-version }}
+
+      - name: Build stefgen
+        run: |
+          cd stefgen
+          make build
+
+      - name: Generate Java code from schemas
+        run: |
+          cd stefgen/generator
+          go test -run TestGenerate
+
+      - name: Run Java tests
+        run: |
+          cd java
+          ./gradlew test
+