fix: rethrow astroerrors in image processing (#13407)

Author: ascorbic

.changeset/small-masks-wink.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Displays correct error message when sharp isn't installed

packages/astro/src/assets/build/generate.ts

@@ -279,6 +279,9 @@ export async function generateImagesForPath(
 				)
 			).data;
 		} catch (e) {
+			if (AstroError.is(e)) {
+				throw e;
+			}
 			const error = new AstroError(
 				{
 					...AstroErrorData.CouldNotTransformImage,