[Gradle] Lower deprecation level of KotlinCompilation source method

It makes IDE Import failing when method is used.
So tooling diagnostic with ERROR level is preferred in such cases.

^KT-58234 Verification Pending

libraries/tools/kotlin-gradle-plugin-api/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/KotlinCompilation.kt

@@ -131,7 +131,7 @@ interface KotlinCompilation<out T : KotlinCommonOptionsDeprecated> : Named,
      * Further details:
      * https://kotl.in/compilation-source-deprecation
      */
-    @Deprecated("scheduled for removal with Kotlin 2.0", level = DeprecationLevel.ERROR)
+    @Deprecated("scheduled for removal with Kotlin 2.0")
     fun source(sourceSet: KotlinSourceSet)
 
     fun associateWith(other: KotlinCompilation<*>)

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

@@ -91,7 +91,7 @@ internal class KotlinCompilationImpl constructor(
     override val kotlinSourceSets: ObservableSet<KotlinSourceSet>
         get() = sourceSets.kotlinSourceSets
 
-    @Deprecated("scheduled for removal with Kotlin 2.0", level = DeprecationLevel.ERROR)
+    @Deprecated("scheduled for removal with Kotlin 2.0")
     override fun source(sourceSet: KotlinSourceSet) {
         project.kotlinToolingDiagnosticsCollector.report(project, KotlinCompilationSourceDeprecation(Throwable()))
         sourceSets.source(sourceSet)

libraries/tools/kotlin-gradle-plugin/src/functionalTest/kotlin/org/jetbrains/kotlin/gradle/unitTests/SourceSetCommonizerTargetTest.kt

@@ -217,7 +217,7 @@ class SourceSetCommonizerTargetTest {
         val nativeMain = kotlin.sourceSets.create("nativeMain")
 
         listOf(linux1, linux2).forEach { target ->
-            @Suppress("DEPRECATION_ERROR")
+            @Suppress("DEPRECATION")
             target.compilations.getByName("main").source(nativeMain)
         }
 

libraries/tools/kotlin-gradle-plugin/src/functionalTest/kotlin/org/jetbrains/kotlin/gradle/unitTests/diagnosticsTests/MppDiagnosticsFunctionalTest.kt

@@ -112,7 +112,7 @@ class MppDiagnosticsFunctionalTest {
         checkDiagnosticsWithMppProject("kotlinCompilationSourceDeprecation") {
             kotlin {
                 val customMain = sourceSets.create("customMain")
-                @Suppress("DEPRECATION_ERROR")
+                @Suppress("DEPRECATION")
                 jvm().compilations.create("custom").source(customMain)
             }
         }