Fix FGP's generateLockfiles task always executing its action at configuration time (#162220)

![drake](https://github.com/user-attachments/assets/50ffcda6-263d-48c8-8853-207e757da6e0)

This PR attempts to fix #110559

This PR supersedes #147837

Original attempt at fixing this by @GaryQian: #112723

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- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
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Fixes] where supported.
- [x] All existing and new tests are passing.

packages/flutter_tools/gradle/src/main/groovy/flutter.groovy

@@ -186,13 +186,15 @@ class FlutterPlugin implements Plugin<Project> {
         Project rootProject = project.rootProject
         if (isFlutterAppProject()) {
             rootProject.tasks.register("generateLockfiles") {
-                rootProject.subprojects.each { subproject ->
-                    String gradlew = (OperatingSystem.current().isWindows()) ?
-                        "${rootProject.projectDir}/gradlew.bat" : "${rootProject.projectDir}/gradlew"
-                    rootProject.exec {
-                        workingDir(rootProject.projectDir)
-                        executable(gradlew)
-                        args(":${subproject.name}:dependencies", "--write-locks")
+                doLast {
+                    rootProject.subprojects.each { subproject ->
+                        String gradlew = (OperatingSystem.current().isWindows()) ?
+                            "${rootProject.projectDir}/gradlew.bat" : "${rootProject.projectDir}/gradlew"
+                        rootProject.exec {
+                            workingDir(rootProject.projectDir)
+                            executable(gradlew)
+                            args(":${subproject.name}:dependencies", "--write-locks")
+                        }
                     }
                 }
             }