chore(dependency): add explicit assertj-core dependency while spockframework upgrade to 2.2-groovy-3.0

[j-sandy]

While upgrading spockframework from 2.0-groovy-3.0 to 2.2-groovy-3.0, encountered below errors during test execution of orca-mine module:

/orca/orca-mine/src/test/java/com/netflix/spinnaker/orca/mine/tasks/RegisterCanaryTaskTest.java:22: error: package org.assertj.core.api does not exist
import static org.assertj.core.api.Assertions.assertThatThrownBy;
                                  ^

/orca/orca-mine/src/test/java/com/netflix/spinnaker/orca/mine/tasks/RegisterCanaryTaskTest.java:150: error: cannot find symbol
    assertThatThrownBy(() -> registerCanaryTask.execute(deployCanaryStage))
    ^
  symbol:   method assertThatThrownBy(()->regist[...]tage))
  location: class RegisterCanaryTaskTest

To fix this issue added assertj-core dependency explicitly.

[j-sandy]

$ ./gradlew orca-mine:dI --dependency assertj-core --configuration testCompileClasspath

> Task :orca-mine:dependencyInsight
org.assertj:assertj-core:3.22.0
  Variant compile:
    | Attribute Name                 | Provided | Requested         |
    |--------------------------------|----------|-------------------|
    | org.gradle.status              | release  |                   |
    | org.gradle.category            | library  | library           |
    | org.gradle.libraryelements     | jar      | classes+resources |
    | org.gradle.usage               | java-api | java-api          |
    | org.gradle.dependency.bundling |          | external          |
    | org.gradle.jvm.environment     |          | standard-jvm      |
    | org.gradle.jvm.version         |          | 11                |
   Selection reasons:
      - By constraint
      - Forced

org.assertj:assertj-core:3.22.0
\--- io.spinnaker.kork:kork-bom:7.236.0
     \--- testCompileClasspath

org.assertj:assertj-core:3.23.1 -> 3.22.0
\--- org.junit.platform:junit-platform-testkit:1.9.0
     +--- io.spinnaker.kork:kork-bom:7.236.0
     |    \--- testCompileClasspath
     +--- org.spockframework:spock-core:2.0-groovy-3.0 (requested org.junit.platform:junit-platform-testkit)
     |    +--- testCompileClasspath (requested org.spockframework:spock-core)
     |    \--- io.spinnaker.kork:kork-bom:7.236.0 (*)
     \--- org.junit:junit-bom:5.9.0
          +--- org.spockframework:spock-core:2.0-groovy-3.0 (requested org.junit:junit-bom:5.7.2) (*)
          +--- org.junit.jupiter:junit-jupiter-api:5.9.0
          |    +--- io.spinnaker.kork:kork-bom:7.236.0 (*)
          |    +--- org.junit:junit-bom:5.9.0 (*)
          |    \--- org.junit.jupiter:junit-jupiter-params:5.9.0
          |         +--- testCompileClasspath (requested org.junit.jupiter:junit-jupiter-params)
          |         +--- io.spinnaker.kork:kork-bom:7.236.0 (*)
          |         \--- org.junit:junit-bom:5.9.0 (*)
          +--- org.junit.platform:junit-platform-testkit:1.9.0 (*)
          +--- org.junit.platform:junit-platform-launcher:1.9.0
          |    +--- io.spinnaker.kork:kork-bom:7.236.0 (*)
          |    +--- org.junit.platform:junit-platform-testkit:1.9.0 (*)
          |    \--- org.junit:junit-bom:5.9.0 (*)
          +--- org.junit.platform:junit-platform-engine:1.9.0
          |    +--- io.spinnaker.kork:kork-bom:7.236.0 (*)
          |    +--- org.spockframework:spock-core:2.0-groovy-3.0 (requested org.junit.platform:junit-platform-engine) (*)
          |    +--- org.junit.platform:junit-platform-launcher:1.9.0 (*)
          |    \--- org.junit:junit-bom:5.9.0 (*)
          +--- org.junit.platform:junit-platform-commons:1.9.0
          |    +--- io.spinnaker.kork:kork-bom:7.236.0 (*)
          |    +--- org.junit.jupiter:junit-jupiter-api:5.9.0 (*)
          |    +--- org.junit.platform:junit-platform-engine:1.9.0 (*)
          |    \--- org.junit:junit-bom:5.9.0 (*)
          \--- org.junit.jupiter:junit-jupiter-params:5.9.0 (*)