docs: add 2.6 and 2.7 rows to the compatibility matrix (#21890)
The matrix stopped at 2.5, so it was missing the released 2.6 line and did not
reflect the PyTorch floor raised to >=2.6 in #21851.
Values are taken from the release tags and CI matrices:
- 2.6 (as of 2.6.5): torch >=2.1.0, <2.10.0; CI tests Python 3.10-3.13
- 2.7 (master): torch >=2.6.0, <2.13.0; CI tests torch 2.6-2.13, Python 3.10-3.13