CI: full Java matrix on ubuntu only; macOS/Windows build with Java 11 and 26 (#704)

Author: vharseko

.github/workflows/build.yml

@@ -23,9 +23,16 @@ jobs:
   build-maven:
     runs-on: ${{ matrix.os }}
     strategy:
+      # The full Java sweep runs on ubuntu only; macOS and Windows build with the
+      # minimum supported (11) and the latest (26) Java.
       matrix:
+        os: [ 'ubuntu-latest' ]
         java: [ '11','17','21','25','26']
-        os: [ 'ubuntu-latest', 'macos-latest', 'windows-latest' ]
+        include:
+          - { os: 'macos-latest',   java: '11' }
+          - { os: 'macos-latest',   java: '26' }
+          - { os: 'windows-latest', java: '11' }
+          - { os: 'windows-latest', java: '26' }
       fail-fast: false
     steps:
     - name:  Install wine+rpm for distribution