[JENKINS-73495] Clarify the plugin incompatibility message

The issue submitter suggested that the plugin incompatibility message
would be clearer if it specifically referred to the installed version
of the plugin.  That seems like an easy change to make and if it helps
a few users, that is great.

core/src/main/resources/hudson/Messages.properties

@@ -67,7 +67,7 @@ PluginManager.UnexpectedException=Unexpected exception going through the retryin
 
 
 PluginManager.compatWarning=\
- Warning: The new version of this plugin is marked as incompatible with the installed version. \
+ Warning: The new version of this plugin is marked as incompatible with the installed version of the plugin. \
  This is usually the case because its behavior or APIs changed, or because it uses a different settings format than the installed version. \
  Other plugins with a dependency on this plugin may be incompatible with this update and no longer work as expected, jobs using this plugin may need to be reconfigured, and/or you may not be able to cleanly revert to the prior version without manually restoring old settings. \
  Consult the plugin release notes for details.

core/src/main/resources/hudson/PluginManager/updates.properties

@@ -20,7 +20,7 @@
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 # THE SOFTWARE.
 compatWarning=\
- Warning: The new version of this plugin is marked as incompatible with the installed version. \
+ Warning: The new version of this plugin is marked as incompatible with the installed version of the plugin. \
  This is usually the case because its behavior changed, or because it uses a different settings format than the installed version. \
  Jobs using this plugin may need to be reconfigured, and/or you may not be able to cleanly revert to the prior version without manually restoring old settings. \
  Consult the plugin release notes for details.