modify the sub-component dirichletbc

As pointed out by @lclaire, the mathematics in
https://jsdokken.com/dolfinx-tutorial/chapter3/component_bc.html#boundary-conditions
is a bit inaccurate, as I state

while what we enforce is

which excludes the to right node.

This should be changed to:
```python
def right(x):
return np.logical_and(np.isclose(x[0], L), x[1] <= H + 1e-14)
```
or
```python
def right(x):
return np.isclose(x[0], L)
```
to be accurate