Add FSL 6.0.7.20, 6.0.7.21, 6.0.7.22 to fsl template

[m9h]

Summary

• Add three missing FSL releases to the fsl.yaml template: 6.0.7.20, 6.0.7.21, 6.0.7.22
• All use the same fslinstaller.py installer as existing 6.0.7.x entries
• 6.0.7.22 (released 2026-03-27) includes applywarp performance/memory improvements and XTRACT fixes

Release notes: https://fsl.fmrib.ox.ac.uk/fsl/docs/development/history/index.html

🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request updates the FSL template in neurodocker/templates/fsl.yaml by adding download URLs for versions 6.0.7.20, 6.0.7.21, and 6.0.7.22. I have no feedback to provide as there were no review comments to evaluate.