citra_qt/main: make SPEED_LIMIT_STEP static constexpr

MSVC does not seem to like using constexpr values in a lambda that were declared outside of it.
Previously on MSVC build the hotkeys to inc-/decrease the speed limit were not working correctly because in the lambda the SPEED_LIMIT_STEP had garbage values.
After googling around a bit I found: https://github.com/codeplaysoftware/computecpp-sdk/issues/95 which seems to be a similar issue.
Trying the suggested fix to make the variable static constexpr also fixes the bug here.

src/yuzu/main.cpp

@@ -561,7 +561,10 @@ void GMainWindow::InitializeHotkeys() {
                 Settings::values.use_frame_limit = !Settings::values.use_frame_limit;
                 UpdateStatusBar();
             });
-    constexpr u16 SPEED_LIMIT_STEP = 5;
+    // TODO: Remove this comment/static whenever the next major release of
+    // MSVC occurs and we make it a requirement (see:
+    // https://developercommunity.visualstudio.com/content/problem/93922/constexprs-are-trying-to-be-captured-in-lambda-fun.html)
+    static constexpr u16 SPEED_LIMIT_STEP = 5;
     connect(hotkey_registry.GetHotkey("Main Window", "Increase Speed Limit", this),
             &QShortcut::activated, this, [&] {
                 if (Settings::values.frame_limit < 9999 - SPEED_LIMIT_STEP) {