fix display and confint of bootstrap for models without dispersion parameter

[palday]

• fix display and confint of bootstrap for models without dispersion parameter

• NEWS

• patch not minor

(cherry picked from commit ec7b986)

• add entry in NEWS.md
• after opening this PR, add a reference and run docs/NEWS-update.jl to update the cross-references.
• I've bumped the version appropriately

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.28%. Comparing base (2974509) to head (70f10a0).
⚠️ Report is 1 commits behind head on v4.x.

Additional details and impacted files

@@           Coverage Diff           @@
##             v4.x     #862   +/-   ##
=======================================
  Coverage   96.27%   96.28%           
=======================================
  Files          38       38           
  Lines        3654     3660    +6     
=======================================
+ Hits         3518     3524    +6     
  Misses        136      136           

Flag	Coverage Δ
current	95.95% <100.00%> (+<0.01%)	⬆️
minimum	96.28% <100.00%> (+<0.01%)	⬆️
nightly	95.90% <100.00%> (+<0.01%)	⬆️

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