fix ci workflow

Author: simonmichael

.github/workflows/ci.yml

@@ -41,11 +41,11 @@ jobs:
     steps:
 
     - name: Check out
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
 
     - name: Cache stack global package db
       id:   stack-global
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       with:
         path: ~/.stack
         key: ${{ runner.os }}-stack-global-${{ matrix.plan.ghc }}-${{ hashFiles('**.yaml') }}
@@ -54,15 +54,15 @@ jobs:
 
     - name: Cache stack-installed programs in ~/.local/bin
       id:   stack-programs
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       with:
         path: ~/.local/bin
         key: ${{ runner.os }}-stack-programs-${{ matrix.plan.ghc }}-${{ hashFiles('**.yaml') }}
         restore-keys: |
              ${{ runner.os }}-stack-programs-${{ matrix.plan.ghc }}
 
     - name: Cache .stack-work
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       with:
         path: .stack-work
         key: ${{ runner.os }}-stack-work-${{ matrix.plan.ghc }}-${{ hashFiles('**.yaml') }}