github: workflows: Refactor upstream build workflow

This updates the manifest in the upstream build workflow before setting up
the Zephyr project. This way the manifest is correct from the very
beginning, speeding up the setup process. The manifest is also updated
using a YAML processor, which is more robust.

Signed-off-by: Kalle Kietäväinen <[email protected]>

.github/workflows/upstream-build.yml

@@ -22,21 +22,18 @@ jobs:
         run: |
           pip3 install crc
 
+      - name: Update manifest to point at upstream main branch
+        working-directory: zephyr-silabs
+        shell: bash
+        run: |
+          yq -i '(.manifest.projects[] | select(.name == "zephyr") | .revision) = "main"' west.yml
+
       - name: Setup Zephyr project
         uses: zephyrproject-rtos/action-zephyr-setup@v1
         with:
           app-path: zephyr-silabs
           toolchains: arm-zephyr-eabi
 
-      - name: Update manifest to point at upstream main branch
-        working-directory: zephyr-silabs
-        shell: bash
-        run: |
-          Z_REV=`west list zephyr -f {revision}`
-          sed s/$Z_REV/main/ west.yml > west.yml.new
-          mv west.yml.new west.yml
-          west update
-
       - name: Fetch blobs
         working-directory: zephyr-silabs
         shell: bash