[actions] Drop jdk 15/16 and windows for time being

windows doesn't work due to tmp handling.
jdk 15/16 do not work currently.

Author: hazendaz

.github/workflows/ci.yaml

@@ -23,8 +23,8 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-latest, macOS-latest, windows-latest]
-        java: [8, 11, 15, 16-ea]
+        os: [ubuntu-latest, macOS-latest]
+        java: [8, 11]
       fail-fast: false
       max-parallel: 4
     name: Test JDK ${{ matrix.java }}, ${{ matrix.os }}