test(datagrid): accept the observed value font and editor settings in the source guards

[datlechin]

#2940 merged one commit short: this fix was committed locally and not pushed yet, so main fails the "Stored value font" suite.

#2940 made views observe the shared ThemeEngine and AppSettingsManager, which changed the text two source guards match:

• standaloneValueViewsResolveTheValueFont required the literal ThemeEngine.shared.valueFont. A view now reads it through the themeEngine it observes, and a static helper still reads the shared engine, so the guard accepts either spelling.
• jsonEditorWatchesEveryAppearanceChange required onChange(of: AppSettingsManager.shared.editor). That form never fired: the value onChange(of:) compares is read while the body is built, and the body did not observe the settings. The guard now requires the observed manager and onChange(of: settingsManager.editor).

ValueFontTests passes locally, 7 cases.