build: also run tests with java8

tests/docker-compose.test.yml

@@ -1,14 +0,0 @@
-version: "3.8"
-
-services:
-  monitor:
-    depends_on:
-      - mc
-    image: itzg/mc-monitor:${MC_MONITOR_VERSION:-0.10.4}
-    command: --debug status --host mc --retry-interval 1s --retry-limit 240
-  mc:
-    restart: "no"
-    image: ${IMAGE_TO_TEST:-itzg/minecraft-server}
-    environment:
-      EULA: "TRUE"
-

tests/docker-compose.yml

@@ -11,4 +11,5 @@ services:
     image: ${IMAGE_TO_TEST:-itzg/minecraft-server}
     environment:
       EULA: "TRUE"
+      VERSION: ${MINECRAFT_VERSION:-LATEST}