[Azure Functions] Update Datadog.Serverless.Compat version to 1.2.0 (#8108)

## Summary of changes

Update `Datadog.Serverless.Compat` to
[v1.2.0](https://github.com/DataDog/datadog-serverless-compat-dotnet/releases/tag/v1.2.0)
for `Datadog.AzureFunctions`.

## Reason for change

New Serverless Compatibility Layer package available.

## Implementation details

## Test coverage

## Other details
<!-- Fixes #{issue} -->


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Author: duncanpharvey

tracer/src/Datadog.AzureFunctions/Datadog.AzureFunctions.csproj

@@ -31,7 +31,7 @@
     <ProjectReference Include="$(MSBuildThisFileDirectory)..\Datadog.Trace.Annotations\Datadog.Trace.Annotations.csproj" />
 
     <!-- Use PrivateAssets="none" to stop excluding content files by default -->
-    <PackageReference Include="Datadog.Serverless.Compat" Version="1.1.2" PrivateAssets="none" />
+    <PackageReference Include="Datadog.Serverless.Compat" Version="1.2.0" PrivateAssets="none" />
 
     <!-- managed assemblies -->
     <None Include="$(SourcePath)/net6.0/Datadog.Trace.dll" Pack="true" Visible="false" PackagePath="contentFiles/any/any/datadog/net6.0/">