Pin git client plugin 3.12.4 for Jenkins 2.332.x tests (#1643)

https://issues.jenkins.io/browse/JENKINS-70174 notes that the git client
plugin automated tests failed when using a shallow clone (depth == 1)
of a single branch.  The issue was fixed for Jenkins 2.346.3 and newer
with the release of git client plugin 3.13.1.  This release is a backport
of that fix.

No plugin functionality was changed in this release.  It changes the
automated tests when run from a shallow clone (depth == 1) of a single
branch.

#1613 is the key consumer in the
plugin bill of materials.

jenkinsci/plugin-compat-tester#382 is the key
consumer in the plugin compatibility tester.

bom-2.332.x/pom.xml

@@ -88,7 +88,7 @@
             <dependency>
                 <groupId>org.jenkins-ci.plugins</groupId>
                 <artifactId>git-client</artifactId>
-                <version>3.12.2</version>
+                <version>3.12.4</version>
             </dependency>
             <dependency>
                 <groupId>org.jenkins-ci.plugins</groupId>