Make :verifyPlugin less strict to fix build failure

As of IDEA version 251.18673.35 (EAP), the task failed because
NixUsageSearcher is using LeafOccurrenceMapper.withPointer, and
LeafOccurrenceMapper has been annotated with @OverrideOnly. Since
withPointer is a static method, I don't think it was intended that this
method is affected. I created IJPL-176605 about the issue.

Anyway, since this is not the first time that I run into some issue with
the strict custom failure levels, I will just revert the option back to
default. Note that non-default failure levels are mostly just warnings,
and don't prevent the plugin from working. There is also no way to
whitelist individual failures, since ignoredProblemsFile seems to work
for compatibility problems only.

Author: JojOatXGME

build.gradle.kts

@@ -2,9 +2,7 @@ import org.jetbrains.changelog.Changelog
 import org.jetbrains.changelog.markdownToHTML
 import org.jetbrains.intellij.platform.gradle.IntelliJPlatformType
 import org.jetbrains.intellij.platform.gradle.TestFrameworkType
-import org.jetbrains.intellij.platform.gradle.tasks.VerifyPluginTask.FailureLevel
 import org.jetbrains.kotlin.gradle.dsl.JvmTarget
-import java.util.EnumSet
 
 plugins {
     id("java")
@@ -122,13 +120,6 @@ intellijPlatform {
                     .orElse(ProductReleasesValueSource())
             )
         }
-        failureLevel = EnumSet.complementOf(
-            EnumSet.of(
-                FailureLevel.DEPRECATED_API_USAGES,
-                FailureLevel.SCHEDULED_FOR_REMOVAL_API_USAGES,
-                FailureLevel.EXPERIMENTAL_API_USAGES,
-            )
-        )
     }
     publishing {
         token = providers.environmentVariable("JETBRAINS_TOKEN")