patch 8.2.5004: right shift on negative number does not work as documented

Problem:    Right shift on negative number does not work as documented.
Solution:   Use a uvarnumber_T type cast.
diff --git a/src/vim9execute.c b/src/vim9execute.c
index b4fd9d5..5410aa2 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -4096,12 +4096,7 @@
 			case EXPR_RSHIFT: if (arg2 > MAX_LSHIFT_BITS)
 					      res = 0;
 					  else
-					  {
-					      res = arg1 >> arg2;
-					      // clear the topmost sign bit
-					      res &= ~((uvarnumber_T)1
-							   << MAX_LSHIFT_BITS);
-					  }
+					      res = (uvarnumber_T)arg1 >> arg2;
 					  break;
 			default: break;
 		    }