Install sbt via coursier in build workflow (#910)

The ubuntu-latest runner image no longer pre-installs sbt, causing
"sbt: command not found" failures. Replace the JDK setup with
coursier/setup-action which installs both the JVM and sbt — mirroring
the approach already used by release_40x.yml on master.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: sksamuel

.github/workflows/build.yml

@@ -20,10 +20,11 @@ jobs:
         with:
           fetch-depth: 0
 
-      - name: Set up JDK
-        uses: actions/setup-java@v1
+      - name: Set up SBT
+        uses: coursier/setup-action@v1
         with:
-          java-version: 11
+          apps: sbt
+          jvm: temurin:11
 
       - name: Import GPG key
         id: import_gpg
@@ -56,10 +57,11 @@ jobs:
         with:
           fetch-depth: 0
 
-      - name: Set up JDK
-        uses: actions/setup-java@v1
+      - name: Set up SBT
+        uses: coursier/setup-action@v1
         with:
-          java-version: 11
+          apps: sbt
+          jvm: temurin:11
 
       - name: Import GPG key
         id: import_gpg