fix: don't ignore mousePressEvent in SplitInput (#4177)

Co-authored-by: Felanbird <41973452+Felanbird@users.noreply.github.com>
Co-authored-by: pajlada <rasmus.karlsson@pajlada.com>
Fixes https://github.com/Chatterino/chatterino2/issues/3844

src/widgets/splits/SplitInput.hpp

@@ -87,6 +87,8 @@ protected:
     void paintEvent(QPaintEvent * /*event*/) override;
     void resizeEvent(QResizeEvent * /*event*/) override;
 
+    void mousePressEvent(QMouseEvent *event) override;
+
     virtual void giveFocus(Qt::FocusReason reason);
 
     QString handleSendMessage(std::vector<QString> &arguments);