Use consistent indent size in Compile Examples workflow

The initial single space indent made the workflow difficult to edit and harmed readability.

Author: per1234

.github/workflows/compile-examples.yml

@@ -4,20 +4,20 @@ on:
   - pull_request
 
 jobs:
- build:
-   runs-on: ubuntu-latest
+  build:
+    runs-on: ubuntu-latest
 
-   strategy:
-     matrix:
-       fqbn:
-         - arduino:samd:mkrwifi1010
-         - arduino:samd:nano_33_iot
-         - arduino:megaavr:uno2018:mode=on
-         - arduino:mbed:nano33ble
+    strategy:
+      matrix:
+        fqbn:
+          - arduino:samd:mkrwifi1010
+          - arduino:samd:nano_33_iot
+          - arduino:megaavr:uno2018:mode=on
+          - arduino:mbed:nano33ble
 
-   steps:
-     - uses: actions/checkout@v2
-     - uses: arduino/compile-sketches@v1
-       with:
-        github-token: ${{ secrets.GITHUB_TOKEN }}
-         fqbn: ${{ matrix.fqbn }}
+    steps:
+      - uses: actions/checkout@v2
+      - uses: arduino/compile-sketches@v1
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          fqbn: ${{ matrix.fqbn }}