Bugfix in BasisFunctionComputation

[frazane]

Type of changes

• Bug fix
• New feature
• Documentation / docstrings
• Tests
• Other

Checklist

• I've formatted the new code by running poetry run pre-commit run --all-files --show-diff-on-failure before committing.
• I've added tests for new code.
• I've added docstrings for the new code.

Description

The scaling was only applied to one of the arguments here:

GPJax/gpjax/kernels/computations/basis_functions.py

Lines 31 to 34 in 549270f

	z1 = self.compute_features(x)
	z2 = self.compute_features(y)
	z1 /= self.kernel.num_basis_fns
	return self.kernel.base_kernel.variance * jnp.matmul(z1, z2.T)

but should be applied outside the matrix computation. This PR fixes this.

Issue Number: N/A