ci: factorize Java version as workflow-level env variable

Replace matrix.java in linux and benchmark jobs with a single
JAVA_VERSION env variable defined at the workflow level.
Also fix benchmark job which was referencing matrix.java without
defining it, and correct linux job name (JDK 8 → JDK 17).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: arey

.github/workflows/main.yml

@@ -9,20 +9,20 @@ on:
     branches:
       - '*'
 
+env:
+  JAVA_VERSION: '17'
+
 jobs:
   linux:
-    name: 'Linux (JDK 8)'
+    name: 'Linux (JDK 17)'
     runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        java: [ '17' ]
 
     steps:
       - uses: actions/checkout@v4.1.1
-      - name: Set up JDK ${{matrix.java}}
+      - name: Set up JDK ${{ env.JAVA_VERSION }}
         uses: actions/setup-java@v4
         with:
-          java-version: ${{matrix.java}}
+          java-version: ${{ env.JAVA_VERSION }}
           distribution: 'adopt'
           cache: maven
       - name: 'Test'
@@ -37,10 +37,10 @@ jobs:
         mapper: [Manual, MapStruct, Selma, JMapper, datus, Orika, ModelMapper, BULL, Dozer, ReMap]
     steps:
       - uses: actions/checkout@v4.1.1
-      - name: Set up JDK ${{matrix.java}}
+      - name: Set up JDK ${{ env.JAVA_VERSION }}
         uses: actions/setup-java@v4
         with:
-          java-version: ${{matrix.java}}
+          java-version: ${{ env.JAVA_VERSION }}
           distribution: 'adopt'
           cache: maven
       - name: 'Install'