Bump R package version to 1.7.3. (#8649)

Author: trivialfis

R-package/DESCRIPTION

@@ -1,8 +1,8 @@
 Package: xgboost
 Type: Package
 Title: Extreme Gradient Boosting
-Version: 1.7.2.1
-Date: 2022-12-08
+Version: 1.7.3.1
+Date: 2023-01-06
 Authors@R: c(
   person("Tianqi", "Chen", role = c("aut"),
          email = "[email protected]"),
@@ -66,5 +66,5 @@ Imports:
     methods,
     data.table (>= 1.9.6),
     jsonlite (>= 1.0),
-RoxygenNote: 7.2.1
+RoxygenNote: 7.2.2
 SystemRequirements: GNU make, C++14