Ignore RST299 warning in tesseroid example (#571)

Make CI happy by ignoring RST299 in one of the examples.

Author: santisoler

doc/gallery_src/forward/tesseroid.py

@@ -15,7 +15,7 @@
 tesseroid on a computation grid through the :func:`harmonica.tesseroid_gravity`
 function.
 
-"""  # noqa: RST399
+"""  # noqa: RST399,RST299
 import boule as bl
 import pygmt
 import verde as vd