GitHub Actions: Use actions/cache@v4 and ubuntu-24.04

.github/workflows/check-format.yaml

@@ -8,7 +8,7 @@ jobs:
       - uses: actions/checkout@v4
       - name: Cache smlfmt
         id: cache-smlfmt
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: ~/.local/bin
           key: ${{ runner.os }}-smlfmt

.github/workflows/ci.yaml

@@ -3,33 +3,13 @@ name: ci
 jobs:
   build-and-test:
     name: build-and-test
-    runs-on: ubuntu-20.04 # 22.04 doesn't contain mlton
+    runs-on: ubuntu-24.04
     steps:
       - uses: actions/checkout@v4
       - name: Install dependencies
         run: |
           sudo apt-get update
-          sudo apt-get install mlton luajit
-      # ubuntu-20.04 has Lua 5.3.3 as lua5.3, which is buggy.
-      - name: Cache Lua 5.3 binary
-        id: cache-lua53
-        uses: actions/cache@v3
-        env:
-          cache-name: cache-lua5.3.6
-        with:
-          path: ~/.local/bin
-          key: ${{ runner.os }}-build-${{ env.cache-name }}
-          restore-keys: ${{ runner.os }}-build-${{ env.cache-name }}
-      - if: ${{ steps.cache-lua53.outputs.cache-hit != 'true' }}
-        name: Build Lua 5.3.6
-        run: |
-          curl -LO https://www.lua.org/ftp/lua-5.3.6.tar.gz
-          tar xf lua-5.3.6.tar.gz
-          cd lua-5.3.6
-          make -j linux
-          mkdir -p ~/.local/bin
-          cp src/lua ~/.local/bin/
-          cp src/luac ~/.local/bin/
+          sudo apt-get install mlton lua5.3 luajit
       - name: Build
         run: make
       - name: Test (Lua)