fix: pin mermaid version in help package

[manel27]

What was done

Since the error is:

 ./node_modules/mermaid/dist/mindmap-definition-44684416.js:4:0-56 - Error: Module not found: Error: "./dist/cytoscape.umd.js" is not exported under the 
conditions ["es2020","es2015","import","module","webpack","production","browser"] from package 
/home/runner/work/cli/cli/scaffolding-validation/Cmf.Custom.Help/node_modules/cytoscape (see exports field in 
/home/runner/work/cli/cli/scaffolding-validation/Cmf.Custom.Help/node_modules/cytoscape/package.json)

The package mermaid was pinned in the help package.

Validation checklist

Please ensure the following conditions are met in order for this PR to be merged:

• Code validation (careful with side-effects)
• Integration test run provided
• Main WorkItem is linked
• Target branch version is correct