Fix progress bar jump between loading states

Author: zaguiini

.stylelintrc

@@ -51,6 +51,7 @@
 			"fr",
 			"ms",
 			"px",
+			"lh",
 			"rem",
 			"s",
 			"vh",

packages/onboarding/src/step-container-v2/components/Heading/style.scss

@@ -16,6 +16,10 @@
 		line-height: 1.25;
 		text-wrap: balance;
 
+		// This ensures that the heading is always at least as tall as the line height.
+		// Useful in case of empty loading titles so we don't see the progress bar jump around.
+		min-height: 1lh;
+
 		&:not( .small ) {
 			@include break-large {
 				font-size: 2.75rem;