Bump org.junit.jupiter:junit-jupiter from 5.11.4 to 5.12.1 in /Plan (#4013)

* Bump org.junit.jupiter:junit-jupiter from 5.11.4 to 5.12.1 in /Plan

Bumps [org.junit.jupiter:junit-jupiter](https://github.com/junit-team/junit5) from 5.11.4 to 5.12.1.
- [Release notes](https://github.com/junit-team/junit5/releases)
- [Commits](junit-team/junit-framework@r5.11.4...r5.12.1)

---
updated-dependencies:
- dependency-name: org.junit.jupiter:junit-jupiter
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

* Fix JUnit not discovering tests

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Aurora Lahtela <24460436+AuroraLS3@users.noreply.github.com>

Author: dependabot[bot]

Plan/build.gradle

@@ -90,7 +90,7 @@ subprojects {
         placeholderapiVersion = "2.11.5"
         nkPlaceholderapiVersion = "1.4-SNAPSHOT"
 
-        junitVersion = "5.11.4"
+        junitVersion = "5.12.1"
         mockitoVersion = "5.16.1"
         seleniumVersion = "4.30.0"
         testContainersVersion = "1.20.6"
@@ -119,6 +119,9 @@ subprojects {
         annotationProcessor("com.google.dagger:dagger-compiler:$daggerVersion") {
             exclude group: "org.jspecify", module: "jspecify"
         }
+
+        // Required for JUnit to discover tests in modules.
+        testRuntimeOnly("org.junit.platform:junit-platform-launcher")
     }
 
     test {