Don't upload multiple times to same artifact in "Compare Performance"…

… workflow

The "Compare Performance" GitHub Actions workflow is configured to time indexing runs at the tip ref, and then do the same for the base ref. The times are then compared to provide information regarding whether a proposed change would have a significant performance impact. This is done by using a job matrix in the GitHub Actions workflow to
perform each of the runs in a parallel GitHub Actions workflow job. A GitHub Actions workflow artifact was used to
transfer the files containing the data for each run between sequential jobs in the workflow. The
"actions/upload-artifact" and "actions/download-artifact" actions are used for this purpose.

Previously, a single artifact was used for the transfer of all the files, with each of the parallel jobs uploading its
own generated files to that artifact. However, support for uploading multiple times to a single artifact was dropped in
version 4.0.0 of the "actions/upload-artifact" action. So it is now necessary to use a dedicated artifact for each of
the builds. These can be downloaded in aggregate by using the artifact name globbing and merging features which were
introduced in version 4.1.0 of the "actions/download-artifact" action.

.github/workflows/compare-performance.yml

@@ -1,7 +1,7 @@
 name: Compare Performance
 
 env:
-  REPORTS_ARTIFACT_NAME: reports
+  REPORTS_ARTIFACT_PREFIX: reports-
 
 # See: https://docs.github.com/en/free-pro-team@latest/actions/reference/events-that-trigger-workflows
 on:
@@ -85,16 +85,20 @@ jobs:
       matrix:
         data:
           # Use two copies of each job to catch job-specific anomalous durations.
-          - ref: ${{ github.ref }} # The tip of the branch selected in the workflow dispatch dialog's "Use workflow from" menu
+          - artifact-suffix: tip-run-1
+            ref: ${{ github.ref }} # The tip of the branch selected in the workflow dispatch dialog's "Use workflow from" menu
             description: tip run 1
             position: after
-          - ref: ${{ github.ref }}
+          - artifact-suffix: tip-run-2
+            ref: ${{ github.ref }}
             description: tip run 2
             position: after
-          - ref: ${{ needs.init.outputs.base-ref }}
+          - artifact-suffix: comparison-run-1
+            ref: ${{ needs.init.outputs.base-ref }}
             description: comparison run 1
             position: before
-          - ref: ${{ needs.init.outputs.base-ref }}
+          - artifact-suffix: comparison-run-2
+            ref: ${{ needs.init.outputs.base-ref }}
             description: comparison run 2
             position: before
 
@@ -298,7 +302,7 @@ jobs:
         with:
           if-no-files-found: error
           path: ${{ env.REPORTS_PATH }}
-          name: ${{ env.REPORTS_ARTIFACT_NAME }}
+          name: ${{ env.REPORTS_ARTIFACT_PREFIX }}${{ matrix.data.ref }}
 
   results:
     needs: run
@@ -312,8 +316,9 @@ jobs:
       - name: Download reports
         uses: actions/download-artifact@v4
         with:
-          name: ${{ env.REPORTS_ARTIFACT_NAME }}
+          merge-multiple: true
           path: ${{ env.REPORTS_PATH }}
+          pattern: ${{ env.REPORTS_ARTIFACT_PREFIX }}*
 
       - name: Print results
         shell: python