[ci] Fix errors with Julia environment

.github/workflows/qa.yaml

@@ -8,6 +8,9 @@ on:
     pull_request:
         types: ['opened', 'synchronize', 'reopened']
 
+env:
+    JULIA_PROJECT: .
+
 jobs:
     qa-ubuntu-conda:
         runs-on: ubuntu-latest
@@ -37,10 +40,12 @@ jobs:
                   miniforge-version: latest
                   mamba-version: '*'
                   python-version: ${{ matrix.python-version }}
-            - name: Setup Julia
+            - name: Set up Julia
               uses: julia-actions/setup-julia@v2
               with:
                   version: '1.10'
+            - name: Cache Julia artifacts
+              uses: julia-actions/cache@v2
             - name: Activate Julia environment
               run: |
                   julia --project=. -e "using Pkg; Pkg.instantiate()"