Fix bad grammar in Buf.push test descriptions

S03-operators/buf.t

@@ -119,19 +119,19 @@ ok Buf.new.subbuf(0, 1) eqv Buf.new(), "subbuf on an empty buffer";
     $a.push(@items);
 
     is $a.elems, 6, "Buf .elems correct after pushing a list";
-    is $a[4], 5, "Buf penultimate element correct after push a list";
-    is $a[5], 6, "Buf last element correct after push a list";
+    is $a[4], 5, "Buf penultimate element correct after pushing a list";
+    is $a[5], 6, "Buf last element correct after pushing a list";
 
     $a.push(7, 8);
 
     is $a.elems, 8, "Buf .elems correct after pushing varargs";
-    is $a[6], 7, "Buf penultimate element correct after push varargs";
-    is $a[7], 8, "Buf last element correct after push varargs";
+    is $a[6], 7, "Buf penultimate element correct after pushing varargs";
+    is $a[7], 8, "Buf last element correct after pushing varargs";
 
     $a.push(9 xx 1);
 
     is $a.elems, 9, "Buf .elems correct after pushing Parcel";
-    is $a[8], 9, "Buf last element correct after push Parcel";
+    is $a[8], 9, "Buf last element correct after pushing Parcel";
 }
 
 # RT #123928