fix: check if content layer files have changed before writing (#12962)

.changeset/light-meals-press.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Skips updating content layer files if content is unchanged

packages/astro/src/content/mutable-data-store.ts

@@ -212,6 +212,11 @@ export default new Map([\n${lines.join(',\n')}]);
 
 		const tempFile = filePath instanceof URL ? new URL(`${filePath.href}.tmp`) : `${filePath}.tmp`;
 		try {
+			const oldData = await fs.readFile(filePath, 'utf-8').catch(() => '');
+			if (oldData === data) {
+				// If the data hasn't changed, we can skip the write
+				return;
+			}
 			// Write it to a temporary file first and then move it to prevent partial reads.
 			await fs.writeFile(tempFile, data);
 			await fs.rename(tempFile, filePath);