Bump io.spring.nullability:io.spring.nullability.gradle.plugin

Bumps [io.spring.nullability:io.spring.nullability.gradle.plugin](https://github.com/spring-gradle-plugins/nullability-plugin) from 0.0.12 to 0.0.13.
- [Release notes](https://github.com/spring-gradle-plugins/nullability-plugin/releases)
- [Commits](spring-gradle-plugins/nullability-plugin@v0.0.12...v0.0.13)

---
updated-dependencies:
- dependency-name: io.spring.nullability:io.spring.nullability.gradle.plugin
  dependency-version: 0.0.13
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

buildSrc/build.gradle

@@ -95,7 +95,7 @@ dependencies {
     implementation 'com.github.spullara.mustache.java:compiler:0.9.14'
     implementation 'io.spring.javaformat:spring-javaformat-gradle-plugin:0.0.47'
     implementation 'io.spring.gradle:spring-security-release-plugin:1.0.15'
-    implementation 'io.spring.nullability:io.spring.nullability.gradle.plugin:0.0.12'
+    implementation 'io.spring.nullability:io.spring.nullability.gradle.plugin:0.0.13'
     implementation 'io.spring.nohttp:nohttp-gradle:0.0.11'
     implementation 'net.sourceforge.htmlunit:htmlunit:2.70.0'
     implementation 'org.asciidoctor:asciidoctor-gradle-jvm:4.0.5'