fixed the git url

Author: mpasserini

.github/workflows/main.yml

@@ -39,6 +39,6 @@ jobs:
       - name: Install MIDI library
         run: arduino-cli lib install "MIDI [email protected]"
       - name: Install StackArray library
-        run: arduino-cli lib install --git-url "https://github.com/oogre/StackArray"
+        run: arduino-cli lib install --git-url "https://github.com/oogre/StackArray.git"
       - name: Compile Sketch
         run: arduino-cli compile --fqbn arduino:avr:mega ./arduino_monotron.ino --warnings more