docs: Update outdated documentation of `Context` (#3561)

docs/content/docs/basics/program-structure.mdx

@@ -145,7 +145,7 @@ The
 type provides the instruction with access to the following non-argument inputs:
 
 ```rust
-pub struct Context<'a, 'b, 'c, 'info, T> {
+pub struct Context<'a, 'b, 'c, 'info, T: Bumps> {
     /// Currently executing program id.
     pub program_id: &'a Pubkey,
     /// Deserialized accounts.
@@ -156,7 +156,8 @@ pub struct Context<'a, 'b, 'c, 'info, T> {
     /// Bump seeds found during constraint validation. This is provided as a
     /// convenience so that handlers don't have to recalculate bump seeds or
     /// pass them in as arguments.
-    pub bumps: BTreeMap<String, u8>,
+    /// Type is the bumps struct generated by #[derive(Accounts)]
+    pub bumps: T::Bumps,
 }
 ```