Fix GuiFont test

We are observing a failing test for font changes

1. the finished signal for the call to vim_command is not caught by the
   signal spy

The root of the issues seems to be a failure to set the font due to some
combination of bad font metrics happening in the test environment. The
GuiFont command was changed to force the change. The timeout was also
increased.

test/tst_shell.cpp

@@ -110,7 +110,7 @@ void TestShell::guiShimCommands() noexcept
 	QObject::connect(c->neovimObject(), &NeovimApi1::err_vim_command_output, SignalPrintError);
 
 	QSignalSpy cmd_font(
-		c->neovimObject()->vim_command_output(c->encode("GuiFont")), &MsgpackRequest::finished);
+		c->neovimObject()->vim_command_output(c->encode("GuiFont!")), &MsgpackRequest::finished);
 	QVERIFY(cmd_font.isValid());
 	QVERIFY2(SPYWAIT(cmd_font), "Waiting for GuiFont");
 
@@ -121,7 +121,7 @@ void TestShell::guiShimCommands() noexcept
 	QVERIFY2(SPYWAIT(cmd_ls), "Waiting for GuiLinespace");
 
 	// Test font attributes
-	const QString cmdFontSize14{ QStringLiteral("GuiFont %1:h14").arg(GetPlatformTestFont()) };
+	const QString cmdFontSize14{ QStringLiteral("GuiFont! %1:h14").arg(GetPlatformTestFont()) };
 	const QString expectedFontSize14{ QStringLiteral("%1:h14").arg(GetPlatformTestFont()) };
 	QSignalSpy cmd_gf{ c->neovimObject()->vim_command_output(c->encode(cmdFontSize14)),
 		&MsgpackRequest::finished };
@@ -137,17 +137,17 @@ void TestShell::guiShimCommands() noexcept
 
 	// Normalization removes the :b attribute
 	const QString cmdFontBoldRemoved{
-		QStringLiteral("GuiFont %1:h14:b:l").arg(GetPlatformTestFont())
+		QStringLiteral("GuiFont! %1:h16:b:l").arg(GetPlatformTestFont())
 	};
-	const QString expectedFontBoldRemoved{ QStringLiteral("%1:h14:l").arg(GetPlatformTestFont()) };
+	const QString expectedFontBoldRemoved{ QStringLiteral("%1:h16:l").arg(GetPlatformTestFont()) };
 	QSignalSpy spy_fontchange2(w->shell(), &ShellWidget::shellFontChanged);
 	QSignalSpy cmd_gf2{ c->neovimObject()->vim_command_output(c->encode(cmdFontBoldRemoved)),
 						&MsgpackRequest::finished };
 	QVERIFY(cmd_gf2.isValid());
 	QVERIFY(SPYWAIT(cmd_gf2, 5000));
 
 	// Test Performance: timeout occurs often, set value carefully.
-	SPYWAIT(spy_fontchange2, 2500 /*msec*/);
+	SPYWAIT(spy_fontchange2, 5000 /*msec*/);
 
 	QCOMPARE(w->shell()->fontDesc(), expectedFontBoldRemoved);
 }