Update .github/workflows/build.yml

This is to avoid this warning during the build Action on github:
The `set-output` command is deprecated and will be disabled soon. Please
upgrade to using Environment Files. For more information see:
https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

Based on recommendation from Discord:
https://discord.com/channels/719497620560543766/719909884769992755/1064004263644233868

build.yml source:
https://github.com/zmkfirmware/unified-zmk-config-template/blob/9a67b2507d2f3a18973d30e5d938e148c727083f/.github/workflows/build.yml

.github/workflows/build.yml

@@ -1,90 +1,5 @@
 on: [push, pull_request, workflow_dispatch]
 
-name: Build
-
 jobs:
-  matrix:
-    runs-on: ubuntu-latest
-    name: Fetch Build Keyboards
-    outputs:
-      matrix: ${{ steps.set-matrix.outputs.matrix }}
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v2
-      - name: Install yaml2json
-        run: python3 -m pip install remarshal
-      - id: set-matrix
-        name: Fetch Build Matrix
-        run: |
-          matrix=$(yaml2json build.yaml | jq -c .)
-          yaml2json build.yaml
-          echo "::set-output name=matrix::${matrix}"
   build:
-    runs-on: ubuntu-latest
-    container:
-      image: zmkfirmware/zmk-build-arm:stable
-    needs: matrix
-    name: Build
-    strategy:
-      fail-fast: false
-      matrix: ${{fromJson(needs.matrix.outputs.matrix)}}
-    steps:
-      - name: Prepare variables
-        id: variables
-        run: |
-          if [ -n "${{ matrix.shield }}" ]; then
-            EXTRA_CMAKE_ARGS="-DSHIELD=${{ matrix.shield }}"
-            ARTIFACT_NAME="${{ matrix.shield }}-${{ matrix.board }}-zmk"
-            DISPLAY_NAME="${{ matrix.shield }} - ${{ matrix.board }}"
-          else
-            EXTRA_CMAKE_ARGS=
-            DISPLAY_NAME="${{ matrix.board }}"
-            ARTIFACT_NAME="${{ matrix.board }}-zmk"
-          fi
-          echo ::set-output name=extra-cmake-args::${EXTRA_CMAKE_ARGS}
-          echo ::set-output name=artifact-name::${ARTIFACT_NAME}
-          echo ::set-output name=display-name::${DISPLAY_NAME}
-      - name: Checkout
-        uses: actions/checkout@v2
-      - name: Cache west modules
-        uses: actions/cache@v2
-        env:
-          cache-name: cache-zephyr-modules
-        with:
-          path: |
-            modules/
-            tools/
-            zephyr/
-            bootloader/
-            zmk/
-          key: ${{ runner.os }}-build-${{ env.cache-name }}-${{ hashFiles('manifest-dir/west.yml') }}
-          restore-keys: |
-            ${{ runner.os }}-build-${{ env.cache-name }}-
-            ${{ runner.os }}-build-
-            ${{ runner.os }}-
-      - name: West Init
-        run: west init -l config
-      - name: West Update
-        run: west update
-      - name: West Zephyr export
-        run: west zephyr-export
-      - name: West Build (${{ steps.variables.outputs.display-name }})
-        run: |
-          west build -s zmk/app -b ${{ matrix.board }} -- -DZMK_CONFIG=${GITHUB_WORKSPACE}/config ${{ steps.variables.outputs.extra-cmake-args }} ${{ matrix.cmake-args }}
-      - name: ${{ steps.variables.outputs.display-name }} Kconfig file
-        run: cat build/zephyr/.config | grep -v "^#" | grep -v "^$"
-      - name: Rename artifacts
-        run: |
-          mkdir build/artifacts
-          if [ -f build/zephyr/zmk.uf2 ]
-          then
-            cp build/zephyr/zmk.uf2 "build/artifacts/${{ steps.variables.outputs.artifact-name }}.uf2"
-          elif [ -f build/zephyr/zmk.hex ]
-          then
-            cp build/zephyr/zmk.hex "build/artifacts/${{ steps.variables.outputs.artifact-name }}.hex"
-          fi
-      - name: Archive (${{ steps.variables.outputs.display-name }})
-        uses: actions/upload-artifact@v2
-        with:
-          name: firmware
-          path: build/artifacts
+    uses: zmkfirmware/zmk/.github/workflows/build-user-config.yml@main