Building Riok.Mapperly.IntegrationTests fails with "Generator 'MapperGenerator' failed to generate source..." in VS 2022.17.11.4

[IanKemp]

Describe the bug
As title.

Additional context
Running msbuild -fl from the root of the repo yields

  Microsoft (R) Visual C# Compiler version 4.11.0-3.24460.3 (5649376e)
  Copyright (C) Microsoft Corporation. All rights reserved.
CSC : warning CS8785: Generator 'MapperGenerator' failed to generate source. It will not contribute to the output and compilation errors may occur as a result. Exception was of type 'InvalidOperationException' with message 'Collection was modified; enumeration operation may not execute.'. [<redacted>\mapperly\test\Riok.Mapperly.IntegrationTests\Riok.Mapperly.IntegrationTests.csproj]
  System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
  at System.Collections.Generic.HashSet`1.Enumerator.MoveNext()
  at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
  at System.Linq.Enumerable.WhereEnumerableIterator`1.MoveNext()
  at Riok.Mapperly.Descriptors.MappingBodyBuilders.ObjectMemberMappingBodyBuilder.BuildMappingBody(MappingBuilderContext ctx, IMemberAssignmentTypeMapping mapping) in /_/src/Riok.Mapperly/Descriptors/MappingBodyBuilders/ObjectMemberMappingBodyBuilder.cs:line 21
  at Riok.Mapperly.Descriptors.MappingBodyBuilders.MappingBodyBuilder.BuildMappingBodies(CancellationToken cancellationToken) in /_/src/Riok.Mapperly/Descriptors/MappingBodyBuilders/MappingBodyBuilder.cs:line 39
  at Riok.Mapperly.Descriptors.DescriptorBuilder.Build(CancellationToken cancellationToken) in /_/src/Riok.Mapperly/Descriptors/DescriptorBuilder.cs:line 86
  at Riok.Mapperly.MapperGenerator.BuildDescriptor(CompilationContext compilationContext, MapperDeclaration mapperDeclaration, MapperConfiguration mapperDefaults, CancellationToken cancellationToken) in /_/src/Riok.Mapperly/MapperGenerator.cs:line 87
  at Riok.Mapperly.MapperGenerator.<>c.<Initialize>b__2_3(ValueTuple`2 x, CancellationToken ct) in /_/src/Riok.Mapperly/MapperGenerator.cs:line 55
  at Microsoft.CodeAnalysis.TransformNode`2.<>c__DisplayClass6_0.<.ctor>b__0(TInput i, CancellationToken token)
  at Microsoft.CodeAnalysis.TransformNode`2.UpdateStateTable(Builder builder, NodeStateTable`1 previousTable, CancellationToken cancellationToken)

The offending method ObjectMemberMappingBodyBuilder.BuildMappingBody(MappingBuilderContext, IMemberAssignmentTypeMapping) contains the following code:

        // init only members should not result in unmapped diagnostics for existing target mappings
        foreach (var initOnlyTargetMember in mappingCtx.EnumerateUnmappedTargetMembers().Where(x => x.IsInitOnly))
        {
            mappingCtx.SetTargetMemberMapped(initOnlyTargetMember);
        }

Forcing an explicit materialisation of the collection used in this foreach fixes the issue and all tests pass:

foreach (var initOnlyTargetMember in mappingCtx.EnumerateUnmappedTargetMembers().Where(x => x.IsInitOnly).ToArray())

This is similar to #1403 and its fix #1438.