Raise minimum Java version from 8 to 11

The load-balancing 2.0.1 library is compiled for Java 11 (class file
version 55.0). Update CI workflows to use Java 11 while keeping the
compilation target at Java 8 for maximum compatibility.

Author: dkropachev

.github/workflows/tests-aws.yml

@@ -34,7 +34,7 @@ jobs:
       - uses: actions/setup-java@v4
         with:
           distribution: temurin
-          java-version: 8
+          java-version: 11
           cache: sbt
       - uses: sbt/setup-sbt@v1
       - name: Download assembly JAR

.github/workflows/tests.yml

@@ -31,7 +31,7 @@ jobs:
       - uses: actions/setup-java@v4
         with:
           distribution: temurin
-          java-version: 8
+          java-version: 11
           cache: sbt
       - uses: sbt/setup-sbt@v1
       - name: Check formatting