Bump Npgsql from 4.0.5 to 4.0.6

Bumps [Npgsql](https://github.com/npgsql/npgsql) from 4.0.5 to 4.0.6.
- [Release notes](https://github.com/npgsql/npgsql/releases)
- [Commits](https://github.com/npgsql/npgsql/compare/v4.0.5...v4.0.6)

Signed-off-by: dependabot[bot] <support@dependabot.com>

OhmGraphite/OhmGraphite.csproj

@@ -30,7 +30,7 @@
   <ItemGroup>
     <PackageReference Include="Costura.Fody" Version="3.3.2" />
     <PackageReference Include="NLog.Config" Version="4.6.2" />
-    <PackageReference Include="Npgsql" Version="4.0.5" />
+    <PackageReference Include="Npgsql" Version="4.0.6" />
     <PackageReference Include="prometheus-net" Version="3.1.1" />
     <PackageReference Include="Resourcer.Fody" Version="1.7.3" />
     <PackageReference Include="TopShelf" Version="4.2.0" />