Bump System.Collections.Immutable from 1.7.1 to 9.0.0 in /src

Bumps [System.Collections.Immutable](https://github.com/dotnet/runtime) from 1.7.1 to 9.0.0.
- [Release notes](https://github.com/dotnet/runtime/releases)
- [Commits](https://github.com/dotnet/runtime/commits/v9.0.0)

---
updated-dependencies:
- dependency-name: System.Collections.Immutable
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

src/Hyperledger.Aries/Hyperledger.Aries.csproj

@@ -19,7 +19,7 @@
         <PackageReference Include="Polly" Version="$(PollyVersion)" />
         <PackageReference Include="Portable.BouncyCastle" Version="1.9.0" />
         <PackageReference Include="Stateless" Version="$(StatelessVersion)" />
-        <PackageReference Include="System.Collections.Immutable" Version="1.7.1" />
+        <PackageReference Include="System.Collections.Immutable" Version="9.0.0" />
         <PackageReference Include="System.IdentityModel.Tokens.Jwt" Version="6.25.1" />
         <PackageReference Include="System.Reactive.Linq" Version="$(SystemReactiveLinqVersion)" />
     </ItemGroup>