Set CI matrix strategy "fail-fast" to false

This property defaults to 'true', and means that if one test fails the remaining tests will halt automatically.

Since each test is testing a different compilation mode / feature / board, I'm disabling this so we get the most information possible out of each commit on failure.

.github/workflows/ci.yml

@@ -12,6 +12,7 @@ jobs:
     runs-on: ubuntu-latest
 
     strategy:
+      fail-fast: false
       matrix:
         board: ['Arduino Leonardo (Serial)', 'Arduino Leonardo (XInput)', 'Teensy 3.2', 'Teensy 4.0']
         include: