Fix import map typing

[MarcSkovMadsen]

Fix _importmap typing as they are on the form

_importmap = {
        "imports": {
            "mermaid": f"https://cdn.jsdelivr.net/npm/mermaid@{VERSION}/dist/mermaid.esm.min.mjs"
        }
    }

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.21%. Comparing base (ef31354) to head (e99c283).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7392      +/-   ##
==========================================
+ Coverage   82.19%   82.21%   +0.01%     
==========================================
  Files         337      337              
  Lines       50514    50514              
==========================================
+ Hits        41522    41529       +7     
+ Misses       8992     8985       -7     

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