fix: install --lockfile-only should exit early (#4932)

ref #4910

.changeset/metal-wasps-impress.md

@@ -0,0 +1,6 @@
+---
+"@pnpm/core": patch
+"pnpm": patch
+---
+
+Return early when the lockfile is up-to-date.

packages/core/src/install/index.ts

@@ -265,7 +265,6 @@ export async function mutateModules (
       opts.frozenLockfileIfExists && ctx.existsWantedLockfile
     if (
       !ctx.lockfileHadConflicts &&
-      !opts.lockfileOnly &&
       !opts.update &&
       !opts.fixLockfile &&
       installsOnly &&
@@ -289,6 +288,9 @@ export async function mutateModules (
           hint: 'Note that in CI environments this setting is true by default. If you still need to run install in such cases, use "pnpm install --no-frozen-lockfile"',
         })
       }
+      if (opts.lockfileOnly) {
+        return projects
+      }
       if (!ctx.existsWantedLockfile) {
         if (ctx.projects.some((project) => pkgHasDependencies(project.manifest))) {
           throw new Error(`Headless installation requires a ${WANTED_LOCKFILE} file`)