test: fix unstable snap-test (#365)

Author: fengmk2

packages/cli/snap-tests/command-lib-monorepo/packages/hello/tsdown.config.ts

@@ -1,4 +1,4 @@
 export default {
   entry: 'src/index.ts',
-  format: ['esm', 'cjs'],
+  format: ['cjs'],
 };

packages/cli/snap-tests/command-lib-monorepo/snap.txt

@@ -4,10 +4,8 @@
 ℹ Using tsdown config: <cwd>/packages/hello/tsdown.config.ts
 ℹ entry: src/index.ts
 ℹ Build start
-ℹ [ESM] dist/index.mjs  <variable> kB │ gzip: <variable> kB
-ℹ [ESM] 1 files, total: <variable> kB
-ℹ [CJS] dist/index.cjs  <variable> kB │ gzip: <variable> kB
-ℹ [CJS] 1 files, total: <variable> kB
+ℹ dist/index.cjs  <variable> kB │ gzip: <variable> kB
+ℹ 1 files, total: <variable> kB
 ✔ Build complete in <variable>ms
 
 
@@ -27,18 +25,15 @@ Task Details:
 
 > ls packages/hello/dist # should have the library
 index.cjs
-index.mjs
 
 > vite run hello#build # should hit cache
 ~/packages/hello$ vite lib (✓ cache hit, replaying)
 ℹ tsdown v<semver> powered by rolldown v<semver>
 ℹ Using tsdown config: <cwd>/packages/hello/tsdown.config.ts
 ℹ entry: src/index.ts
 ℹ Build start
-ℹ [ESM] dist/index.mjs  <variable> kB │ gzip: <variable> kB
-ℹ [ESM] 1 files, total: <variable> kB
-ℹ [CJS] dist/index.cjs  <variable> kB │ gzip: <variable> kB
-ℹ [CJS] 1 files, total: <variable> kB
+ℹ dist/index.cjs  <variable> kB │ gzip: <variable> kB
+ℹ 1 files, total: <variable> kB
 ✔ Build complete in <variable>ms