use checkout v3 in downstream tests (#133)

Author: jishnub

.github/workflows/downstream.yml

@@ -23,14 +23,14 @@ jobs:
           - {repo: ApproxFunSingularities.jl, group: JuliaApproximation}
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: julia-actions/setup-julia@v1
         with:
           version: ${{ matrix.julia-version }}
           arch: x64
       - uses: julia-actions/julia-buildpkg@latest
       - name: Clone Downstream
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
         with:
           repository: ${{ matrix.package.group }}/${{ matrix.package.repo }}
           path: downstream