Bump most of the actions for node20.

We can't bump haskell-actions/setup yet because there isn't a node20 version of it.

.github/workflows/ci.yml

@@ -17,25 +17,25 @@ jobs:
         ghc: ["8.4", "8.6", "8.8", "8.10", "9.0", "9.2", "9.4", "9.6"]
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
       if: github.event.action == 'opened' || github.event.action == 'synchronize' || github.event.ref == 'refs/heads/main'
 
     - uses: haskell-actions/setup@v2
       name: Setup Haskell
       with:
         ghc-version: ${{ matrix.ghc }}
 
-    - uses: actions/cache@v2
+    - uses: actions/cache@v4
       name: Cache ~/.cabal/packages
       with:
         path: ~/.cabal/packages
         key: ${{ runner.os }}-${{ matrix.ghc }}-cabal-packages
-    - uses: actions/cache@v2
+    - uses: actions/cache@v4
       name: Cache ~/.cabal/store
       with:
         path: ~/.cabal/store
         key: ${{ runner.os }}-${{ matrix.ghc }}-cabal-store
-    - uses: actions/cache@v2
+    - uses: actions/cache@v4
       name: Cache dist-newstyle
       with:
         path: dist-newstyle