Upgrade GitHub Actions versions

Author: mykelk

.github/workflows/ci.yml

@@ -27,12 +27,12 @@ jobs:
         arch:
           - x64
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: julia-actions/setup-julia@v1
         with:
           version: ${{ matrix.version }}
           arch: ${{ matrix.arch }}
-      - uses: actions/cache@v1
+      - uses: actions/cache@v4
         env:
           cache-name: cache-artifacts
         with:
@@ -68,7 +68,7 @@ jobs:
     name: Documentation
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       # TexLive installation
       - name: Install TexLive
         run: sudo apt-get install pdf2svg texlive-latex-base texlive-binaries texlive-pictures texlive-latex-extra texlive-luatex