AppStatisticsMonitor: Fix missing include on Linux

Amends de18097cb4.

Change-Id: I91d8fcc76ba3bf464f9fc53eabc39704253bd497
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/appstatisticsmonitor/idataprovider.cpp

@@ -11,6 +11,10 @@
 #include <QRegularExpression>
 #include <QString>
 
+#ifdef Q_OS_LINUX
+#include <unistd.h>
+#endif
+
 using namespace Utils;
 
 namespace AppStatisticsMonitor::Internal {