Add missing namespace to MultiComboBox component

[Robbware]

Prerequisites

• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
• I have verified that I am following the COMET-WEB code style guidelines
• I have provided test coverage for my change (where applicable)

Description

Add a missing namespace to the new MultiComboBox component which was blocking the nuget package from being built.

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (8d464e2) 78.31% compared to head (42c9517) 78.31%.
Report is 2 commits behind head on development.

Additional details and impacted files

@@             Coverage Diff              @@
##           development     #465   +/-   ##
============================================
  Coverage        78.31%   78.31%           
============================================
  Files              330      330           
  Lines             7600     7600           
  Branches           772      772           
============================================
  Hits              5952     5952           
  Misses            1414     1414           
  Partials           234      234           

Files	Coverage Δ
COMET.Web.Common/Components/MultiComboBox.razor	61.76% <ø> (ø)

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[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

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