Upgrade Checkstyle 10.20.2 -> 10.21.0 (#1460)

While there, also update the integration test.

See:
- https://checkstyle.sourceforge.io/releasenotes.html
- https://github.com/checkstyle/checkstyle/releases/tag/checkstyle-10.21.0
- https://github.com/checkstyle/checkstyle/compare/checkstyle-10.20.2...checkstyle-10.21.0

integration-tests/checkstyle-init.patch

@@ -13,7 +13,7 @@
      <dependency>
        <groupId>nl.jqno.equalsverifier</groupId>
        <artifactId>equalsverifier</artifactId>
-@@ -2417,9 +2423,13 @@
+@@ -2421,9 +2427,13 @@
                    <compilerArgs>
                      <arg>-Xpkginfo:always</arg>
                      <arg>-XDcompilePolicy=simple</arg>
@@ -27,7 +27,7 @@
                    </compilerArgs>
                    <annotationProcessorPaths>
                      <path>
-@@ -2432,6 +2442,11 @@
+@@ -2436,6 +2446,11 @@
                        <artifactId>error-prone-contrib</artifactId>
                        <version>${error-prone-support.version}</version>
                      </path>
@@ -39,7 +39,7 @@
                    </annotationProcessorPaths>
                  </configuration>
                </execution>
-@@ -2472,11 +2487,14 @@
+@@ -2476,11 +2491,14 @@
                    <compilerArgs>
                      <arg>-Xpkginfo:always</arg>
                      <arg>-XDcompilePolicy=simple</arg>
@@ -55,7 +55,7 @@
                    </compilerArgs>
                    <annotationProcessorPaths>
                      <path>
-@@ -2489,6 +2507,11 @@
+@@ -2493,6 +2511,11 @@
                        <artifactId>error-prone-contrib</artifactId>
                        <version>${error-prone-support.version}</version>
                      </path>

integration-tests/checkstyle.sh

@@ -5,7 +5,7 @@ set -e -u -o pipefail
 test_name="$(basename "${0}" .sh)"
 project='checkstyle'
 repository='https://github.com/checkstyle/checkstyle.git'
-revision='checkstyle-10.20.2'
+revision='checkstyle-10.21.0'
 additional_build_flags='-Perror-prone-compile,error-prone-test-compile -Dmaven.compiler.failOnError=true'
 additional_source_directories='${project.basedir}${file.separator}src${file.separator}it${file.separator}java,${project.basedir}${file.separator}src${file.separator}xdocs-examples${file.separator}java'
 shared_error_prone_flags='-XepExcludedPaths:(\Q${project.basedir}${file.separator}src${file.separator}\E(it|test|xdocs-examples)\Q${file.separator}resources\E|\Q${project.build.directory}${file.separator}\E).*'

pom.xml

@@ -928,7 +928,7 @@
                         <dependency>
                             <groupId>com.puppycrawl.tools</groupId>
                             <artifactId>checkstyle</artifactId>
-                            <version>10.20.2</version>
+                            <version>10.21.0</version>
                         </dependency>
                         <dependency>
                             <groupId>io.spring.nohttp</groupId>