Fixed Java versions for many GitHub actions

Author: fulminazzo

.github/workflows/bukkit-1.13.yml

@@ -9,5 +9,5 @@ jobs:
   test:
     uses: ./.github/workflows/bukkit-test.yml
     with:
-      java-version: 11
+      java-version: 8
       minecraft-version: "1.13.2-R0.1-SNAPSHOT"

.github/workflows/bukkit-1.14.yml

@@ -9,5 +9,5 @@ jobs:
   test:
     uses: ./.github/workflows/bukkit-test.yml
     with:
-      java-version: 11
+      java-version: 8
       minecraft-version: "1.14.4-R0.1-SNAPSHOT"

.github/workflows/bukkit-1.15.yml

@@ -9,5 +9,5 @@ jobs:
   test:
     uses: ./.github/workflows/bukkit-test.yml
     with:
-      java-version: 11
+      java-version: 8
       minecraft-version: "1.15.2-R0.1-SNAPSHOT"

.github/workflows/bukkit-1.16.yml

@@ -9,5 +9,5 @@ jobs:
   test:
     uses: ./.github/workflows/bukkit-test.yml
     with:
-      java-version: 17
+      java-version: 8
       minecraft-version: "1.16.5-R0.1-SNAPSHOT"