[CI] Added build conditions

.github/workflows/main.yml

@@ -19,24 +19,30 @@ jobs:
             board: "arduino:samd:arduino_zero_native"
     
     runs-on: ubuntu-latest
+    env:
+      run-build: ${{ (matrix.board == "arduino:avr:uno") || "contains(github.event.head_commit.message, 'CI_FORCE_BUILD'" || "contains(github.event.head_commit.message, 'Bump version to'" }}
     
     steps:
       - name: Install arduino-cli
+        if: ${{ run-build }}
         run: |
           mkdir -p ~/.local/bin
           echo "::add-path::~/.local/bin"
           curl -fsSL https://raw.githubusercontent.com/arduino/arduino-cli/master/install.sh | BINDIR=~/.local/bin sh
       
       - name: Install platform
+        if: ${{ run-build }}
         run: |
           arduino-cli core update-index
           arduino-cli core install ${{ matrix.platform }}
           echo "::set-env name=WARNINGS::all"
       
       - name: Checkout
+        if: ${{ run-build }}
         uses: actions/checkout@v2
       
       - name: Build all examples
+        if: ${{ run-build }}
         run: |
           for example in $(find $PWD/examples -name '*.ino' | sort); do
             # check whether to skip this sketch