[BUG] Link to "testing.md" is wrong in "pipeline.md"

[elodiegermani]

Describe the bug

The link to testing.md in this file: https://github.com/Inria-Empenn/narps_open_pipelines/blob/main/docs/pipelines.md is wrong (last paragraph).
Need to be updated.

Reproduction

1. Go to https://github.com/Inria-Empenn/narps_open_pipelines/blob/main/docs/pipelines.md
2. Scroll till the end of the file
3. Click on "testing topic of the documentation"

Expected behavior

This should lead to https://github.com/Inria-Empenn/narps_open_pipelines/blob/main/docs/testing.md

NARPS Open Pipeline version

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Operating System

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Softwares versions

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Screenshots

No response