Fix typos in JuliaSyntax.mk (#51210)
before
```
x@x julia % make -C deps fastcheck-JuliaSyntax
make: *** No rule to make target `fastcheck-JuliaSyntax'. Stop.
x@x julia % make -C deps fastcheck-JuliSyntax
make: *** No rule to make target `compile-JuliSyntax', needed by `check-JuliSyntax'. Stop.
```
after
```
x@x julia % make -C deps fastcheck-JuliaSyntax
make: Nothing to be done for `fastcheck-JuliaSyntax'.
```
Co-authored-by: Lilith Hafner <Lilith.Hafner@gmail.com>
