Bump actions/download-artifact from 4 to 6

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 4 to 6.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v4...v6)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -130,7 +130,7 @@ jobs:
         run: ./sbt +update
 
       - name: Download target directories (2.12, rootJS)
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
         with:
           name: target-${{ matrix.os }}-${{ matrix.java }}-2.12-rootJS
 
@@ -140,7 +140,7 @@ jobs:
           rm targets.tar
 
       - name: Download target directories (2.12, rootJVM)
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
         with:
           name: target-${{ matrix.os }}-${{ matrix.java }}-2.12-rootJVM
 
@@ -150,7 +150,7 @@ jobs:
           rm targets.tar
 
       - name: Download target directories (2.12, rootNative)
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
         with:
           name: target-${{ matrix.os }}-${{ matrix.java }}-2.12-rootNative
 
@@ -160,7 +160,7 @@ jobs:
           rm targets.tar
 
       - name: Download target directories (2.13, rootJS)
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
         with:
           name: target-${{ matrix.os }}-${{ matrix.java }}-2.13-rootJS
 
@@ -170,7 +170,7 @@ jobs:
           rm targets.tar
 
       - name: Download target directories (2.13, rootJVM)
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
         with:
           name: target-${{ matrix.os }}-${{ matrix.java }}-2.13-rootJVM
 
@@ -180,7 +180,7 @@ jobs:
           rm targets.tar
 
       - name: Download target directories (2.13, rootNative)
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
         with:
           name: target-${{ matrix.os }}-${{ matrix.java }}-2.13-rootNative
 
@@ -190,7 +190,7 @@ jobs:
           rm targets.tar
 
       - name: Download target directories (3, rootJS)
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
         with:
           name: target-${{ matrix.os }}-${{ matrix.java }}-3-rootJS