downgrade ubuntu in CI

Author: pjfanning

.github/workflows/ci.yml

@@ -22,7 +22,7 @@ jobs:
     name: Build and Test
     strategy:
       matrix:
-        os: [ubuntu-latest]
+        os: [ubuntu-20.04]
         scala: [2.11.12, 2.12.20, 2.13.15, 3.3.4]
         java: [zulu@8]
     runs-on: ${{ matrix.os }}
@@ -40,9 +40,6 @@ jobs:
           java-version: 8
           cache: sbt
 
-      - name: Setup sbt
-        uses: actions/setup-sbt-installer@v1
-
       - name: Scala 2.13 build
         if: startsWith(matrix.scala, '2.13')
         run: sbt '++ ${{ matrix.scala }}' coverage test coverageReport
@@ -84,9 +81,6 @@ jobs:
           java-version: 8
           cache: sbt
 
-      - name: Setup sbt
-        uses: actions/setup-sbt-installer@v1
-
       - name: Download target directories (2.11.12)
         uses: actions/download-artifact@v4
         with: