use java 21, addressing comment @enebo:wq

Author: seuros

.github/workflows/ruby.yml

@@ -46,6 +46,11 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
+      - name: Set up Java 21
+        uses: actions/setup-java@v4
+        with:
+          distribution: 'temurin'
+          java-version: '21'
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with:
@@ -103,6 +108,11 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
+      - name: Set up Java 21
+        uses: actions/setup-java@v4
+        with:
+          distribution: 'temurin'
+          java-version: '21'
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with:
@@ -138,6 +148,11 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
+      - name: Set up Java 21
+        uses: actions/setup-java@v4
+        with:
+          distribution: 'temurin'
+          java-version: '21'
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with:
@@ -180,6 +195,11 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
+      - name: Set up Java 21
+        uses: actions/setup-java@v4
+        with:
+          distribution: 'temurin'
+          java-version: '21'
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with:
@@ -231,6 +251,11 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
+      - name: Set up Java 21
+        uses: actions/setup-java@v4
+        with:
+          distribution: 'temurin'
+          java-version: '21'
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with:
@@ -260,6 +285,11 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
+      - name: Set up Java 21
+        uses: actions/setup-java@v4
+        with:
+          distribution: 'temurin'
+          java-version: '21'
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with: