Build Truth and its Javadoc under Java 26, and test under {8, 17, 25} instead of {8, 11}.

This half-matches Guava, where:
- We build under Java 26, albeit with a different approach (cl/711476575, cl/711746683).
- We test under those versions plus 11, I think because we do some stuff with old versions of Gradle there (cl/912590939).

Motivation:
- Newer javac and javadoc binaries are good.
- Building on a version higher than Java 8 is necessary for module support (#1601).
- We will hopefully someday want to conditionally use newer libraries.
RELNOTES=n/a
PiperOrigin-RevId: 916187164

Author: cpovirk

.github/workflows/ci.yml

@@ -9,11 +9,8 @@ on:
       - master
 
 jobs:
-  test:
-    name: "JDK ${{ matrix.java }}"
-    strategy:
-      matrix:
-        java: [ 8, 11 ]
+  build:
+    name: 'Build with JDK 26'
     runs-on: ubuntu-latest
     steps:
       # Cancel any previous runs for the same branch that are still running.
@@ -23,34 +20,71 @@ jobs:
           access_token: ${{ github.token }}
       - name: 'Check out repository'
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd
-      - name: 'Set up JDK ${{ matrix.java }}'
+      - name: 'Set up JDK 26 for compilation'
         uses: actions/setup-java@be666c2fcd27ec809703dec50e508c2fdc7f6654
         with:
-          java-version: ${{ matrix.java }}
+          java-version: 26
           distribution: 'temurin'
           cache: 'maven'
       - name: 'Install'
         shell: bash
         run: mvn -B -P!standard-with-extra-repos install -U -DskipTests=true
-      - name: 'Test'
-        shell: bash
-        run: mvn -B -P!standard-with-extra-repos verify -U -Dmaven.javadoc.skip=true
       - name: 'Javadoc Test Run'
         shell: bash
         run: mvn -B -P!standard-with-extra-repos javadoc:aggregate -U
+      - name: 'Upload build artifacts'
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a
+        with:
+          name: truth-jars
+          path: |
+            **/target/*.jar
+            !**/target/*-sources.jar
+            !**/target/*-javadoc.jar
+
+  test:
+    name: "Test with JDK ${{ matrix.java }}"
+    needs: build
+    strategy:
+      matrix:
+        java: [ 8, 17, 25 ]
+    runs-on: ubuntu-latest
+    steps:
+      - name: 'Check out repository'
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd
+      - name: 'Set up JDK ${{ matrix.java }} for testing'
+        uses: actions/setup-java@be666c2fcd27ec809703dec50e508c2fdc7f6654
+        with:
+          java-version: ${{ matrix.java }}
+          distribution: 'temurin'
+          cache: 'maven'
+      - name: 'Download build artifacts'
+        uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c
+        with:
+          name: truth-jars
+      - name: 'Unpack artifacts'
+        shell: bash
+        run: |
+          for f in $(find . -name "*.jar" ! -name "*-gwt.jar"); do
+            dest="${f%/target/*}/target/classes"
+            mkdir -p "$dest"
+            unzip -o "$f" -d "$dest"
+          done
+      - name: 'Test'
+        shell: bash
+        run: mvn -B -P!standard-with-extra-repos verify -U -Dmaven.javadoc.skip=true -Dmaven.main.skip=true
 
   publish_snapshot:
     name: 'Publish snapshot'
-    needs: test
+    needs: [build, test]
     if: github.event_name == 'push' && github.repository == 'google/truth'
     runs-on: ubuntu-latest
     steps:
       - name: 'Check out repository'
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd
-      - name: 'Set up JDK 11'
+      - name: 'Set up JDK 26'
         uses: actions/setup-java@be666c2fcd27ec809703dec50e508c2fdc7f6654
         with:
-          java-version: 11
+          java-version: 26
           distribution: 'temurin'
           cache: 'maven'
           server-id: central
@@ -66,16 +100,16 @@ jobs:
     permissions:
       contents: write
     name: 'Generate latest docs'
-    needs: test
+    needs: [build, test]
     if: github.event_name == 'push' && github.repository == 'google/truth'
     runs-on: ubuntu-latest
     steps:
       - name: 'Check out repository'
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd
-      - name: 'Set up JDK 11'
+      - name: 'Set up JDK 26'
         uses: actions/setup-java@be666c2fcd27ec809703dec50e508c2fdc7f6654
         with:
-          java-version: 11
+          java-version: 26
           distribution: 'temurin'
           cache: 'maven'
       - name: 'Generate latest docs'