Add GCC9 to compile matrix

Author: Andy4495

.github/workflows/arduino-compile-sketches.yml

@@ -20,6 +20,10 @@ jobs:
             fqbn: 'arduino:avr:uno'
             platform-name: 'arduino:avr'
             platform-sourceurl: 'https://downloads.arduino.cc/packages/package_index.json'
+          - arch: msp-gcc9
+            fqbn: 'energia:msp430gcc9:MSP-EXP430F5529LP'
+            platform-name: 'energia:msp430gcc9'
+            platform-sourceurl: 'https://raw.githubusercontent.com/Andy4495/TI_Platform_Cores_For_Arduino/refs/heads/main/json/package_energia_minimal_msp430_index.json'
           - arch: msp
             fqbn: 'energia:msp430:MSP-EXP430F5529LP'
             platform-name: 'energia:msp430'