Add <NoWarn>$(NoWarn);NU5128</NoWarn>

One approach is to wrap your <dependencies> in the .nuspec file
with:  <group targetFramework=".NETFramework4.6.2">

The other approach is <NoWarn>$(NoWarn);NU5128</NoWarn>

Since I didn't get anywhere with the first approach, I went with the 2nd.

Refs:

NuGet/docs.microsoft.com-nuget#1677
NuGet/Home#8583 (comment)

src/RimDev.AspNet.Diagnostics.HealthChecks/RimDev.AspNet.Diagnostics.HealthChecks.csproj

@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <Project ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
   <PropertyGroup>
@@ -12,6 +12,7 @@
     <TargetFrameworkVersion>v4.6.2</TargetFrameworkVersion>
     <FileAlignment>512</FileAlignment>
     <Deterministic>true</Deterministic>
+    <NoWarn>$(NoWarn);NU5128</NoWarn>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <DebugSymbols>true</DebugSymbols>