docs: improve language in tuples-and-arrays section (#2875)

I asked Gemini to review the English for inconsistencies and grammar
mistakes. This is the result and I hope it's useful!

As a non-native speaker, it is hard for me to evaluate the finer
details, so let me know if you would like to see changes (or even
better: make them directly in the PR with the suggestion function).

---------

Co-authored-by: Dmitri Gribenko <[email protected]>

Author: mgeisler

src/tuples-and-arrays/arrays.md

@@ -67,7 +67,8 @@ fn main() {
 
 - Arrays are not heap-allocated. They are regular values with a fixed size known
   at compile time, meaning they go on the stack. This can be different from what
-  students expect if they come from a garbage collected language, where arrays
+  students expect if they come from a garbage-collected language, where arrays
   may be heap allocated by default.
 
 </details>
+s>

src/tuples-and-arrays/exercise.md

@@ -12,8 +12,8 @@ let array = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];
 
 What is the type of this variable?
 
-Use an array such as the above to write a function `transpose` which will
-transpose a matrix (turn rows into columns):
+Use an array such as the above to write a function `transpose` that transposes a
+matrix (turns rows into columns):
 
 <!-- mdbook-xgettext: skip -->