CI: unique upload names given immutability

Reference: https://github.com/actions/download-artifact/blob/fa0a91b85d4f404e444e00e005971372dc801d16/docs/MIGRATION.md#multiple-uploads-to-the-same-named-artifact

Author: slivingston

.github/workflows/slycot-build-and-test.yml

@@ -128,8 +128,9 @@ jobs:
       - name: Save wheel
         uses: actions/upload-artifact@v4
         with:
-          name: slycot-wheels
+          name: slycot-wheels-${{ matrix.os }}-${{ matrix.python }}-${{ matrix.bla_vendor }}
           path: slycot-wheels
+          retention-days: 5
 
   build-conda:
     name: Build conda, ${{ matrix.os }}
@@ -178,8 +179,9 @@ jobs:
       - name: Save to local conda pkg channel
         uses: actions/upload-artifact@v4
         with:
-          name: slycot-conda-pkgs
+          name: slycot-conda-pkgs-${{ matrix.os }}-${{ matrix.python }}
           path: slycot-conda-pkgs
+          retention-days: 5
 
   create-wheel-test-matrix:
     name: Create wheel test matrix
@@ -189,6 +191,11 @@ jobs:
     outputs:
       matrix: ${{ steps.set-matrix.outputs.matrix }}
     steps:
+      - name: Merge artifacts
+        uses: actions/upload-artifact/merge@v4
+        with:
+          name: slycot-wheels
+          pattern: slycot-wheels-*
       - name: Checkout Slycot
         uses: actions/checkout@v3
       - name: Download wheels (if any)
@@ -207,6 +214,11 @@ jobs:
     outputs:
       matrix: ${{ steps.set-matrix.outputs.matrix }}
     steps:
+      - name: Merge artifacts
+        uses: actions/upload-artifact/merge@v4
+        with:
+          name: slycot-conda-pkgs
+          pattern: slycot-conda-pkgs-*
       - name: Checkout Slycot
         uses: actions/checkout@v3
       - name: Download conda packages