Create separate tester artifacts for each build

Previously, a single workflow artifact was created by the "Arduino IDE" GitHub Actions workflow. This artifact contained
the builds for each operating system, including all three versions of the Windows build. This resulted in beta testers
needing to do a >1 GB download for every build, even though they likely needed only ~200 MB of what they downloaded.

Producing separate workflows makes it easier for beta testers to participate in the development and is less wasteful of
resources.

.github/workflows/build.yml

@@ -183,3 +183,36 @@ jobs:
           PLUGIN_BUCKET: ${{ secrets.DOWNLOADS_BUCKET }}
           AWS_ACCESS_KEY_ID: ${{ secrets.AWS_ACCESS_KEY_ID }}
           AWS_SECRET_ACCESS_KEY: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
+
+  artifacts:
+    name: ${{ matrix.artifact.name }} artifact
+    needs: build
+    if: always() && needs.build.result != 'skipped'
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        artifact:
+          - path: "*Linux_64bit.zip"
+            name: Linux_X86-64
+          - path: "*macOS_64bit.dmg"
+            name: macOS
+          - path: "*Windows_64bit.exe"
+            name: Windows_X86-64_interactive_installer
+          - path: "*Windows_64bit.msi"
+            name: Windows_X86-64_MSI
+          - path: "*Windows_64bit.zip"
+            name: Windows_X86-64_zip
+
+    steps:
+      - name: Download job transfer artifact
+        uses: actions/download-artifact@v2
+        with:
+          name: ${{ env.JOB_TRANSFER_ARTIFACT }}
+          path: ${{ env.JOB_TRANSFER_ARTIFACT }}
+      
+      - name: Upload tester build artifact
+        uses: actions/upload-artifact@v2
+        with:
+          name: ${{ matrix.artifact.name }}
+          path: ${{ env.JOB_TRANSFER_ARTIFACT }}/${{ matrix.artifact.path }}