Fixed Task group names duplication in Task's task_id for MappedOperator

[evgenii-prusov]

Summary

Fixes task_id duplication when unmapping a MappedOperator within a TaskGroup. Previously, task IDs would get double-prefixed (e.g., tg1.tg1.mapped_task instead of tg1.mapped_task).

Problem

When MappedOperator.unmap() is called, it passes the already-prefixed task_id to BaseOperator.__init__, which applies the prefix again via task_group.child_id().

closes: #52334

Solution

Check if task_id already contains the task group prefix before passing to BaseOperator, preventing double prefixing.

Testing

Added test test_mapped_operator_in_task_group_no_duplicate_prefix to verify the fix. All existing tests pass.

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[boring-cyborg]

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[evgenii-prusov]

@Lee-W , please, have a look

[boring-cyborg]

Awesome work, congrats on your first merged pull request! You are invited to check our Issue Tracker for additional contributions.

[github-actions]

Backport failed to create: v3-0-test. View the failure log Run details

Status	Branch	Result
❌	v3-0-test

You can attempt to backport this manually by running:

cherry_picker 6b618ef v3-0-test

This should apply the commit to the v3-0-test branch and leave the commit in conflict state marking
the files that need manual conflict resolution.

After you have resolved the conflicts, you can continue the backport process by running:

cherry_picker --continue