ci: bump actions/upload-artifact from 4 to 6

.github/workflows/ci.yml

@@ -95,7 +95,7 @@ jobs:
 
       - name: Upload receipt
         if: always()
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: signetry-self-receipt
           path: |

.github/workflows/release.yml

@@ -53,7 +53,7 @@ jobs:
         run: uvx twine check dist/*
 
       - name: Upload build artifacts
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: dist
           path: dist/

.github/workflows/reviewer.yml

@@ -115,7 +115,7 @@ jobs:
 
       - name: Upload the review comment artifact
         if: always()
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: signetry-reviewer-comment
           path: ${{ runner.temp }}/rev-out

.github/workflows/signetry-autofix.yml

@@ -252,7 +252,7 @@ jobs:
               print(f"opened branch-only PR for {branch}")
           PY
 
-      - uses: actions/upload-artifact@v4
+      - uses: actions/upload-artifact@v6
         if: always()
         with:
           name: signetry-autofix