Lock Zephyr version to v4.1.0 (swiftlang#137)

- Locks Zephyr version for nrfx-blink-sdk project to v4.1.0
- Updates invalid -DBOARD definition for Zephyr v4.1.0
- Reenables pull-request workflow for build-zephyr action

Author: xtremekforever

.github/workflows/build-zephyr.yml

@@ -3,6 +3,8 @@ name: Zephyr
 on:
   push:
     branches: ["main"]
+  pull_request:
+    types: [opened, reopened, synchronize, ready_for_review]
   workflow_dispatch:
 
 jobs:

nrfx-blink-sdk/README.md

@@ -23,7 +23,7 @@ This example demonstrates how to integrate with the Zephyr SDK via CMake and how
 ``` console
 $ cd nrfx-blink-sdk
 $ source ~/zephyrproject/.venv/bin/activate
-(.venv) cmake -B build -G Ninja -DBOARD=nrf52840dk_nrf52840 -DUSE_CCACHE=0 .
+(.venv) cmake -B build -G Ninja -DBOARD=nrf52840dk/nrf52840 -DUSE_CCACHE=0 .
 (.venv) cmake --build build
 ```
 

nrfx-blink-sdk/west.yml

@@ -6,7 +6,7 @@ manifest:
   projects:
     - name: zephyr
       remote: zephyrproject-rtos
-      revision: main
+      revision: v4.1.0
       import:
         name-allowlist:
           - cmsis  # required by the ARM port