Bump actions/download-artifact from 5 to 6

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 5 to 6.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v5...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] <[email protected]>

Author: dependabot[bot]

.github/workflows/pull-request-checks.yaml

@@ -157,7 +157,7 @@ jobs:
       - name: Confirm z3 solver is available and log the version installed
         run: z3 --version
       - name: Get the ebmc binary
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           name: ebmc-binary
           path: ebmc
@@ -191,7 +191,7 @@ jobs:
       - name: Confirm ltl2tgba is available and log the version installed
         run: ltl2tgba --version
       - name: Get the ebmc binary
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           name: ebmc-binary
           path: ebmc
@@ -209,7 +209,7 @@ jobs:
     steps:
       - uses: actions/checkout@v5
       - name: Get the ebmc binary
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           name: ebmc-binary
           path: ebmc
@@ -218,7 +218,7 @@ jobs:
       - name: ebmc on Hazard3
         run: PATH=$PATH:$PWD/ebmc examples/Hazard3/Hazard3-ebmc.sh
       - name: Get the vlindex binary
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           name: vlindex-binary
           path: vlindex
@@ -483,17 +483,17 @@ jobs:
       - name: Confirm z3 solver is available and log the version installed
         run: z3 --version
       - name: Get the ebmc binary
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           name: ebmc-binary
           path: bin
       - name: Get the hw-cbmc binary
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           name: hw-cbmc-binary
           path: bin
       - name: Get the vlindex binary
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           name: vlindex-binary
           path: bin