[Gradle] Don't fail when psm is missing from a given included build

This basically restores behaviour as before changes related to
the configuration cache support

See:
https://github.com/JetBrains/kotlin/blob/35dacd6add18e031902765fd1386f9f8aad7e738/libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/KotlinProjectStructureMetadata.kt#L427

^KT-56198 Verification Pending

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/MppDependencyProjectStructureMetadataExtractorFactory.kt

@@ -42,13 +42,10 @@ private constructor(
                 )
             } else {
                 val key = ProjectPathWithBuildName(moduleId.projectPath, moduleId.build.name)
-                val projectStructureMetadataProvider = includedBuildsProjectStructureMetadataProviders.value[key]
-                    ?: error("Project structure metadata not found for project $key")
-
                 IncludedBuildMppDependencyProjectStructureMetadataExtractor(
                     componentId = moduleId,
                     primaryArtifact = metadataArtifact.file,
-                    projectStructureMetadataProvider = projectStructureMetadataProvider::value
+                    projectStructureMetadataProvider = { includedBuildsProjectStructureMetadataProviders.value[key]?.value }
                 )
             }
         } else {