tpl: Add math.Sqrt

Fixes #6941

tpl/math/init.go

@@ -64,6 +64,13 @@ func init() {
 			},
 		)
 
+		ns.AddMethodMapping(ctx.Sqrt,
+			nil,
+			[][2]string{
+				{"{{math.Sqrt 81}}", "9"},
+			},
+		)
+
 		ns.AddMethodMapping(ctx.Mod,
 			[]string{"mod"},
 			[][2]string{