fix: use spatialgeometry's correctly-spelled _propagate_scene_tree()

[petercorke]

Summary

spatialgeometry's _propogate_scene_tree() was a plain misspelling of
"propagate" -- see jhavl/spatialgeometry#38.
That PR was amended before merging: rather than landing a correctly-spelled
but still-private _propagate_scene_tree() only to deprecate it again
immediately after, it went straight to a public update() method.
_propogate_scene_tree() (the original misspelled name this repo called)
remains available as a deprecated (FutureWarning) alias for back-compat,
but this migrates Link.py's and Robot.py's 8 call sites to call
update() directly instead.

Not touching this repo's own vendored src/spatialgeometry/ snapshot --
that's separate, deliberate legacy left alone for now.

Test plan

• Confirmed no collision with any existing RTB method: grepped the
  whole roboticstoolbox tree for def update( -- only unrelated local
  functions elsewhere (PyPlot backends, mobile/Animations.py), none on
  Robot/Link or anywhere in their MRO
• Confirmed live: rtb.Robot.update is spatialgeometry.SceneNode.update
  is True
• Hit an unrelated, pre-existing failure constructing a full URDF robot
  (Panda()) in this environment: Link.py calls
  SceneGroup(scene_children=geometry) directly, which doesn't match
  SceneGroup's actual constructor (initlist, not scene_children) --
  a separate API mismatch, nothing to do with this change. Not chased down
  per your steer on test_Robot.py's existing ~34 unrelated failures.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (30a0264) to head (972ff0d).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/roboticstoolbox/robot/Link.py	0.00%	4 Missing ⚠️
src/roboticstoolbox/robot/Robot.py	0.00%	4 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #570   +/-   ##
=====================================
  Coverage   0.00%   0.00%           
=====================================
  Files        142     142           
  Lines      13825   13827    +2     
=====================================
- Misses     13825   13827    +2     

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