make the tar c command in prepare_package.dart verbose (#139687)

Help debug https://github.com/flutter/flutter/issues/139597

dev/bots/prepare_package/archive_creator.dart

@@ -528,6 +528,8 @@ class ArchiveCreator {
       'tar',
       'cJf',
       output.absolute.path,
+      // Print out input files as they get added, to debug hangs
+      '--verbose',
       path.basename(source.absolute.path),
     ], workingDirectory: fs.directory(path.dirname(source.absolute.path)));
   }

dev/bots/test/prepare_package_test.dart

@@ -159,7 +159,7 @@ void main() {
           if (platform.isWindows) 'attrib -h .git': null,
           if (platform.isWindows) '7za a -tzip -mx=9 $archiveName flutter': null
           else if (platform.isMacOS) 'zip -r -9 --symlinks $archiveName flutter': null
-          else if (platform.isLinux) 'tar cJf $archiveName flutter': null,
+          else if (platform.isLinux) 'tar cJf $archiveName --verbose flutter': null,
         }));
         await creator.initializeRepo();
         await creator.createArchive();
@@ -197,7 +197,7 @@ void main() {
           if (platform.isWindows) 'attrib -h .git': null,
           if (platform.isWindows) '7za a -tzip -mx=9 $archiveName flutter': null
           else if (platform.isMacOS) 'zip -r -9 --symlinks $archiveName flutter': null
-          else if (platform.isLinux) 'tar cJf $archiveName flutter': null,
+          else if (platform.isLinux) 'tar cJf $archiveName --verbose flutter': null,
         };
         processManager.addCommands(convertResults(calls));
         creator = ArchiveCreator(
@@ -247,7 +247,7 @@ void main() {
           if (platform.isWindows) 'attrib -h .git': null,
           if (platform.isWindows) '7za a -tzip -mx=9 $archiveName flutter': null
           else if (platform.isMacOS) 'zip -r -9 --symlinks $archiveName flutter': null
-          else if (platform.isLinux) 'tar cJf $archiveName flutter': null,
+          else if (platform.isLinux) 'tar cJf $archiveName --verbose flutter': null,
         };
         processManager.addCommands(convertResults(calls));
         creator = ArchiveCreator(
@@ -306,7 +306,7 @@ void main() {
           if (platform.isWindows) 'attrib -h .git': null,
           if (platform.isWindows) '7za a -tzip -mx=9 $archiveName flutter': null
           else if (platform.isMacOS) 'zip -r -9 --symlinks $archiveName flutter': null
-          else if (platform.isLinux) 'tar cJf $archiveName flutter': null,
+          else if (platform.isLinux) 'tar cJf $archiveName --verbose flutter': null,
         };
         processManager.addCommands(convertResults(calls));
         creator = ArchiveCreator(