DotNet.ReproducibleBuilds.Isolated breaks builds with source-built .NET SDKs

[omajid]

When using a .NET SDK built via source-build (eg, dotnet-sdk-9.0 package in Fedora), dotnet build is broken when this package is used.

Originally found by @artiomchi at dotnet/core#9859 (comment):

➜ dotnet new console
The template "Console App" was created successfully.

Processing post-creation actions...
Restoring /home/artiom/Dev/_tmp/ConsoleTest/ConsoleTest.csproj:
Restore succeeded.

➜ ## Adding reference to the project file
➜ cat ConsoleTest.csproj 
<Project Sdk="Microsoft.NET.Sdk">

  <Sdk Name="DotNet.ReproducibleBuilds.Isolated" Version="1.2.25" />

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net9.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

</Project>
➜ dotnet build
    /home/artiom/Dev/_tmp/ConsoleTest/ConsoleTest.csproj : error NU1101: Unable to find package Microsoft.NETCore.App.Host.fedora.42-x64. No packages exist with this id in source(s): nuget.org

Restore failed with 1 error(s) in 2.6s
➜ dotnet --info
.NET SDK:
 Version:           9.0.104
 Commit:            7931ad4860
 Workload version:  9.0.100-manifests.dc2cb94f
 MSBuild version:   17.12.27+7931ad486

Runtime Environment:
 OS Name:     fedora
 OS Version:  42
 OS Platform: Linux
 RID:         fedora.42-x64
 Base Path:   /usr/lib64/dotnet/sdk/9.0.104/

.NET workloads installed:
There are no installed workloads to display.
Configured to use loose manifests when installing new manifests.

Host:
  Version:      9.0.3
  Architecture: x64
  Commit:       7931ad4860

.NET SDKs installed:
  8.0.114 [/usr/lib64/dotnet/sdk]
  9.0.104 [/usr/lib64/dotnet/sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 8.0.14 [/usr/lib64/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 9.0.3 [/usr/lib64/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 8.0.14 [/usr/lib64/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 9.0.3 [/usr/lib64/dotnet/shared/Microsoft.NETCore.App]

Other architectures found:
  None

Environment variables:
  DOTNET_ROOT       [/usr/lib64/dotnet]

global.json file:
  Not found

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