Finish Tween explanation in animation tutorial (#12519)

_Description of what this PR is changing or adding, and why:_
Bullet point about Tween animation at the end of the animation tutorial
was not complete. Assumed it was talking generally about the object
being animated. Could also be something like *...object properties being
animated* in this context.

_Issues fixed by this PR (if any):_

_PRs or commits this PR depends on (if any):_

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Author: StephenBrough

src/content/ui/animations/tutorial.md

@@ -654,7 +654,7 @@ class _LogoAppState extends State<LogoApp> with SingleTickerProviderStateMixin {
 * An [`AnimationController`][] manages the `Animation`.
 * A [`CurvedAnimation`][] defines progression as a non-linear curve.
 * A [`Tween`][] interpolates between the range of data as used by the
-  object be
+  object being animated.
 
 ## Next steps