Fix container action errors

Error: Container operations are only supported on Linux runners

Author: liufengyun

Diff for: .github/workflows/ci.yaml

@@ -99,65 +99,15 @@ jobs:
 
   test-windows:
     runs-on: [self-hosted, Windows]
-    container: lampepfl/dotty-windows:2020-10-02
 
     steps:
-      - name: Git Checkout
-        uses: actions/checkout@v2
-
-      - name: Cache Ivy
-        uses: actions/[email protected]
-        with:
-          path: C:\.ivy2\cache
-          key: ${{ runner.os }}-ivy-${{ hashFiles('**/build.sbt') }}
-          restore-keys: ${{ runner.os }}-ivy-
-
-      - name: Cache SBT
-        uses: actions/[email protected]
-        with:
-          path: C:\.sbt
-          key: ${{ runner.os }}-sbt-${{ hashFiles('project/**') }}
-          restore-keys: ${{ runner.os }}-sbt-
-
-      - name: Cache Coursier and Mill
-        uses: actions/[email protected]
-        with:
-          path: C:\.cache
-          key: ${{ runner.os }}-general-${{ hashFiles('**/build.sbt') }}
-          restore-keys: ${{ runner.os }}-general-
-
       - name: Test
         run: sbt ";compile ;test"
 
   test_bootstrapped-windows:
     runs-on: [self-hosted, Windows]
-    container: lampepfl/dotty-windows:2020-10-02
 
     steps:
-      - name: Git Checkout
-        uses: actions/checkout@v2
-
-      - name: Cache Ivy
-        uses: actions/[email protected]
-        with:
-          path: C:\.ivy2\cache
-          key: ${{ runner.os }}-ivy-${{ hashFiles('**/build.sbt') }}
-          restore-keys: ${{ runner.os }}-ivy-
-
-      - name: Cache SBT
-        uses: actions/[email protected]
-        with:
-          path: C:\.sbt
-          key: ${{ runner.os }}-sbt-${{ hashFiles('project/**') }}
-          restore-keys: ${{ runner.os }}-sbt-
-
-      - name: Cache Coursier and Mill
-        uses: actions/[email protected]
-        with:
-          path: C:\.cache
-          key: ${{ runner.os }}-general-${{ hashFiles('**/build.sbt') }}
-          restore-keys: ${{ runner.os }}-general-
-
       - name: Test
         run: sbt ";dotty-bootstrapped/compile ;dotty-bootstrapped/test;sjsJUnitTests/test"