Remove redundant now grgit Gradle plugin

The `grgit` Gradle plugin has been used to determine modified files to update their Copyright.
After migrating to a `-present` pattern we don't need to track modified files anymore.
Therefore, we don't need to manage `org.ajoberstar.grgit` plugin, too.

**Cherry-pick to `3.2.x`**

# Conflicts:
#	.github/dependabot.yml
#	build.gradle

Author: artembilan

.github/dependabot.yml

@@ -17,11 +17,10 @@ updates:
        development-dependencies:
          update-types:
           - patch
-         patterns: 
-         - com.gradle.*
+         patterns:
+         - org.gradle.*
          - com.github.spotbugs
          - io.spring.*
-         - org.ajoberstar.grgit
          - org.antora
          - io.micrometer:micrometer-docs-generator
          - com.willowtreeapps.assertk:assertk-jvm

build.gradle

@@ -18,7 +18,6 @@ buildscript {
 plugins {
 	id 'base'
 	id 'idea'
-	id 'org.ajoberstar.grgit' version '5.3.2'
 	id 'io.spring.nohttp' version '0.0.11'
 	id 'io.spring.dependency-management' version '1.1.7' apply false
 	id 'org.antora' version '1.0.0'
@@ -37,14 +36,6 @@ ext {
 	linkScmConnection = 'git://github.com/spring-projects/spring-amqp.git'
 	linkScmDevConnection = '[email protected]:spring-projects/spring-amqp.git'
 
-	modifiedFiles =
-			files()
-					.from {
-						files(grgit.status().unstaged.modified)
-								.filter { f -> f.name.endsWith('.java') || f.name.endsWith('.kt') }
-					}
-	modifiedFiles.finalizeValueOnRead()
-
 	assertjVersion = '3.26.3'
 	assertkVersion = '0.28.1'
 	awaitilityVersion = '4.2.2'