fix linux build on github actions

[leonardonapoless]

build errors:

Run cmake --build build --config Release
[0/2] Re-checking globbed directories...
[1/46] Building CXX object _deps/clap-juce-extensions-build/CMakeFiles/clap_juce_extensions.dir/src/extensions/clap-juce-extensions.cpp.o
[2/46] Building CXX object CMakeFiles/TrebleMaker.dir/_deps/juce-src/modules/juce_audio_processors/juce_audio_processors_ara.cpp.o
[3/46] Building CXX object CMakeFiles/TrebleMaker.dir/_deps/juce-src/modules/juce_audio_processors/juce_audio_processors_lv2_libs.cpp.o
[4/46] Building CXX object CMakeFiles/TrebleMaker.dir/_deps/juce-src/modules/juce_gui_extra/juce_gui_extra.cpp.o
FAILED: [code=1] CMakeFiles/TrebleMaker.dir/_deps/juce-src/modules/juce_gui_extra/juce_gui_extra.cpp.o
/usr/bin/c++ -DHAS_CLAP_JUCE_EXTENSIONS=1 -DJUCE_GLOBAL_MODULE_SETTINGS_INCLUDED=1 -DJUCE_MODULE_AVAILABLE_juce_audio_basics=1 -DJUCE_MODULE_AVAILABLE_juce_audio_devices=1 -DJUCE_MODULE_AVAILABLE_juce_audio_formats=1 -DJUCE_MODULE_AVAILABLE_juce_audio_plugin_client=1 -DJUCE_MODULE_AVAILABLE_juce_audio_processors=1 -DJUCE_MODULE_AVAILABLE_juce_audio_utils=1 -DJUCE_MODULE_AVAILABLE_juce_core=1 -DJUCE_MODULE_AVAILABLE_juce_data_structures=1 -DJUCE_MODULE_AVAILABLE_juce_dsp=1 -DJUCE_MODULE_AVAILABLE_juce_events=1 -DJUCE_MODULE_AVAILABLE_juce_graphics=1 -DJUCE_MODULE_AVAILABLE_juce_gui_basics=1 -DJUCE_MODULE_AVAILABLE_juce_gui_extra=1 -DJUCE_SHARED_CODE=1 -DJUCE_STANDALONE_APPLICATION=JucePlugin_Build_Standalone -DJUCE_VST3_CAN_REPLACE_VST2=0 -DJucePlugin_AAXCategory=0 -DJucePlugin_AAXDisableBypass=0 -DJucePlugin_AAXDisableMultiMono=0 -DJucePlugin_AAXIdentifier=com.LeoCodes.TrebleMaker -DJucePlugin_AAXManufacturerCode=JucePlugin_ManufacturerCode -DJucePlugin_AAXProductId=JucePlugin_PluginCode -DJucePlugin_ARACompa
/home/runner/work/TrebleMaker/TrebleMaker/build/_deps/juce-src/modules/juce_gui_extra/juce_gui_extra.cpp:127:11: fatal error: gtk/gtk.h: No such file or directory
127 | #include <gtk/gtk.h>
| ^~~~~~~~~~~
compilation terminated.
[5/46] Building CXX object CMakeFiles/TrebleMaker.dir/Source/UI/LookAndFeel.cpp.o
[6/46] Building CXX object CMakeFiles/TrebleMaker.dir/Source/Core/PluginProcessor.cpp.o
[7/46] Building CXX object CMakeFiles/TrebleMaker.dir/Source/UI/PluginEditor.cpp.o
[8/46] Building CXX object CMakeFiles/juce_vst3_helper.dir/_deps/juce-src/modules/juce_audio_plugin_client/VST3/juce_VST3ManifestHelper.cpp.o
[9/46] Building CXX object CMakeFiles/TrebleMaker.dir/_deps/juce-src/modules/juce_audio_processors/juce_audio_processors.cpp.o
ninja: build stopped: subcommand failed.
Error: Process completed with exit code 1.