[test] Use correct FirOutputPartForDependsOnModule for running checkers that run in common session

Review: https://jetbrains.team/p/kt/reviews/14807

Motivation: no motivation, I was just passing by and noticed this bug.

It looks like this commit doesn't affect any tests

compiler/tests-common-new/tests/org/jetbrains/kotlin/test/frontend/fir/handlers/FirDiagnosticsHandler.kt

@@ -643,7 +643,7 @@ open class FirDiagnosticCollectorService(val testServices: TestServices) : TestS
 
             for (part in info.partsForDependsOnModules) {
                 result += part.session.runCheckers(
-                    platformPart.firAnalyzerFacade.scopeSession,
+                    part.firAnalyzerFacade.scopeSession,
                     part.firFiles.values,
                     DiagnosticReporterFactory.createPendingReporter(),
                     mppCheckerKind = MppCheckerKind.Common