Install development package for rigmatrix for Linux in the CI

.github/workflows/c-cpp.yml

@@ -54,6 +54,7 @@ jobs:
       if: runner.os == 'Linux'
       run: |
         sudo apt install libusb-1.0-0-dev
+        sudo apt install libgd-dev
         sudo apt install libgpiod-dev
         sudo apt install libindi-dev libnova-dev
         sudo apt install grep