chore(ci): bump artifact actions

Author: MilesCranmerBot

.github/workflows/CI.yml

@@ -56,7 +56,7 @@ jobs:
         shell: bash
       - name: Upload coverage artifact
         if: success()
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: coverage-${{ matrix.os }}-julia-${{ matrix.julia-version }}
           path: lcov.info
@@ -93,7 +93,7 @@ jobs:
         shell: bash
       - name: Upload coverage artifact
         if: steps.run-tests.outcome == 'success'
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: coverage-${{ matrix.test_name }}-${{ matrix.os }}-julia-${{ matrix.julia-version }}
           path: lcov.info
@@ -107,7 +107,7 @@ jobs:
       - additional_tests
     steps:
       - name: Download coverage artifacts
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v7
         with:
           pattern: coverage-*
           path: coverage