github: workflows: Only build on Linux

Upstream should do a good enough job of testing all supported Zephyr SDK OS
versions. We can reintroduce macOS and Windows if/when we start doing more
advanced things in CI that Zephyr upstream doesn't already do.

Signed-off-by: Johan Hedberg <johan.hedberg@silabs.com>

Author: jhedberg

.github/workflows/build.yml

@@ -10,11 +10,7 @@ on:
 
 jobs:
   build:
-    strategy:
-      fail-fast: false
-      matrix:
-        os: [ubuntu-22.04, macos-14, windows-2022]
-    runs-on: ${{ matrix.os }}
+    runs-on: ubuntu-22.04
     steps:
       - name: Checkout
         uses: actions/checkout@v4

.github/workflows/upstream-build.yml

@@ -6,11 +6,7 @@ on:
 
 jobs:
   build:
-    strategy:
-      fail-fast: false
-      matrix:
-        os: [ubuntu-22.04, macos-14, windows-2022]
-    runs-on: ${{ matrix.os }}
+    runs-on: ubuntu-22.04
     steps:
       - name: Checkout
         uses: actions/checkout@v4