Correct two typos in exercise text (functions, python_by_example)

- functions.md: "Rewrite the function `factorial()` in from [Exercise 1]"
  -> "... `factorial()` from [Exercise 1]"
- python_by_example.md hint: "noted that suppose `var = 42`"
  -> "note that if `var = 42`"

Spotted by Copilot on QuantEcon/lecture-python-programming.ml#14, which
copies exercise blocks byte-for-byte from this repo, so the typos can
only be corrected here.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: mmcky

lectures/functions.md

@@ -669,7 +669,7 @@ print([x(i) for i in range(10)])
 :label: func_ex5
 ```
 
-Rewrite the function `factorial()` in from [Exercise 1](factorial_exercise) using recursion.
+Rewrite the function `factorial()` from [Exercise 1](factorial_exercise) using recursion.
 
 ```{exercise-end}
 ```

lectures/python_by_example.md

@@ -510,7 +510,7 @@ If you can, add a legend, to help distinguish between the three time series.
 :class: dropdown
 
 * If you call the `plot()` function multiple times before calling `show()`, all of the lines you produce will end up on the same figure.
-* For the legend, noted that suppose `var = 42`, the expression `f'foo{var}'` evaluates to `'foo42'`.
+* For the legend, note that if `var = 42`, the expression `f'foo{var}'` evaluates to `'foo42'`.
 ```
 
 ```{exercise-end}