SF-3920 Fix event metrics not being recorded for BuildCompletedAsync

[pmachapman]

This PR fixes a bug I noticed on live where the following error was being logged in the journal:

Error logging event metric for BuildCompletedAsync
System.FormatException: Cannot deserialize a 'BsonDocument' from BsonType 'Int32'.
   at MongoDB.Bson.Serialization.Serializers.BsonValueSerializerBase`1.Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
   at MongoDB.Bson.BsonDocument.Parse(String json)
   at SIL.XForge.Services.EventMetricService.GetBsonValue(Object objectValue) in D:\Source\Repos\web-xforge\src\SIL.XForge\Services\EventMetricService.cs:line 175
   at SIL.XForge.Services.EventMetricService.SaveEventMetricAsync(String projectId, String userId, String eventType, EventScope scope, Dictionary`2 argumentsWithNames, Object result, Nullable`1 executionTime, Exception exception) in D:\Source\Repos\web-xforge\src\SIL.XForge\Services\EventMetricService.cs:line 108
   at SIL.XForge.EventMetrics.EventMetricLogger.<>c__DisplayClass7_0.<<Intercept>g__SaveEventMetricAsync|0>d.MoveNext() in D:\Source\Repos\web-xforge\src\SIL.XForge\EventMetrics\EventMetricLogger.cs:line 189

This error doesn't prevent builds from completing, but will prevent the recording of the BuildCompletedAsync event metric.

---

This change is 

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.94%. Comparing base (1bf3173) to head (90aec91).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4079   +/-   ##
=======================================
  Coverage   80.94%   80.94%           
=======================================
  Files         664      664           
  Lines       42115    42121    +6     
  Branches     6936     6936           
=======================================
+ Hits        34088    34095    +7     
+ Misses       6880     6879    -1     
  Partials     1147     1147           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

[github-actions]

📸 Screenshot diff deployed! (2 changes)

View the visual diff at: https://pr-4079--sf-screenshot-diffs.netlify.app

[RaymondLuong3]

@RaymondLuong3 reviewed 5 files and all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on pmachapman).