fix: remove duplicate layout parent in SidePanelWidget (flameshot-org#4578)

The widget's layout is set in the member initializer list (line 25)
via m_layout(new QVBoxLayout(this)). Passing 'this' to the QHBoxLayout
constructor at line 84 tries to set a second layout on the same widget,
which Qt rejects with a warning on every capture:

  QLayout: Attempting to add QLayout "" to SidePanelWidget "",
  which already has a layout

The parent argument is unnecessary since the layout is added to
m_layout via addLayout() at line 94.

Co-authored-by: Benigno Batista Júnior <benigno@opus-software.com.br>

Author: benignobjunior

src/widgets/panel/sidepanelwidget.cpp

@@ -81,7 +81,7 @@ SidePanelWidget::SidePanelWidget(QPixmap* p, QWidget* parent)
     m_layout->addWidget(m_colorWheel);
     m_layout->addWidget(m_colorHex);
 
-    QHBoxLayout* gridHBoxLayout = new QHBoxLayout(this);
+    QHBoxLayout* gridHBoxLayout = new QHBoxLayout();
     m_gridCheck = new QCheckBox(tr("Display grid"), this);
     m_gridSizeSpin = new QSpinBox(this);
     m_gridSizeSpin->setRange(5, 50);