fix(ci): split elixir package building into own step

Since the job step may run out of execution time, by separating the
Elixir build from the traditional one may prevent timeouts.

.github/workflows/build_packages.yaml

@@ -240,6 +240,12 @@ jobs:
           - 24.1.5-3 # we test with OTP 23, but only build package on OTP 24 versions
         elixir:
           - 1.13.1
+        # used to split elixir packages into a separate job, since the
+        # entire job may take a lot of time, especially on arm64
+        # emulation
+        build_elixir:
+          - with_elixir
+          - no_elixir
         arch:
           - amd64
           - arm64
@@ -341,6 +347,7 @@ jobs:
         PROFILE: ${{ matrix.profile }}
         ARCH: ${{ matrix.arch }}
         SYSTEM: ${{ matrix.os }}
+      if: ${{ matrix.build_elixir == 'no_elixir' }}
       working-directory: source
       # FIXME: use tagged version once merged
       run: |
@@ -362,6 +369,17 @@ jobs:
           --system "${SYSTEM}" \
           --builder "ghcr.io/emqx/emqx-builder/elixir:${ELIXIR}-${OTP}-${SYSTEM}"
 
+    - name: build emqx packages (Elixir)
+      env:
+        OTP: ${{ matrix.otp }}
+        ELIXIR: ${{ matrix.elixir }}
+        PROFILE: ${{ matrix.profile }}
+        ARCH: ${{ matrix.arch }}
+        SYSTEM: ${{ matrix.os }}
+      working-directory: source
+      if: ${{ matrix.build_elixir == 'with_elixir' }}
+      # FIXME: use tagged version once merged
+      run: |
         ./scripts/buildx.sh \
           --profile "${PROFILE}" \
           --pkgtype "elixirpkg" \