fix: correct compile_fail doctest example

[Unique-Usman]

Replace invalid syntax in doctest with Some(42) to properly demonstrate a compile-time error when a non-Result value is passed to assert_err!

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[Unique-Usman]

When I ran just test I got this

error: no rules expected `Some`
 --> crates/floresta-common/src/macros.rs:95:28
  |
7 | assert_err!(Ok::<u32, &str>Some(42));
  |                            ^^^^ no rules expected this token in macro call
  |
  = note: while trying to match sequence start

The test was testing for assert_err when Result value is not passed to it.

After this changes it gave this error

error[E0308]: mismatched types
 --> crates/floresta-common/src/macros.rs:65:1
  |
7 | assert_ok!(Some(42));
  | ^^^^^^^^^^^--------^
  | |          |
  | |          this expression has type `Option<{integer}>`
  | expected `Option<{integer}>`, found `Result<_, _>`
  |
  = note: expected enum `Option<{integer}>`
             found enum `Result<_, _>`
  = note: this error originates in the macro `assert_ok` (in Nightly builds, run with -Z macro-backtrace for more info)

rustc 1.93.0 (254b59607 2026-01-19)