docs(moonbeam-engineering): add compile-with-tests step to cherry-pick verification (#52)

## What

Adds a **"Verify the branch compiles"** step to the `qa-cherry-picks`
skill's `verify-cherry-picks.md`, requiring `cargo check --workspace
--tests` during fork-branch QA.

## Why

The verification flow confirmed cherry-picks via git but never checked
that the fork branch still built. Plain `cargo check --workspace` skips
`#[cfg(test)]` modules and integration tests, so a cherry-pick — or an
upstream refactor it lands on top of — can leave a test module that no
longer compiles while the check still reports success.

This was hit during the stable2603 cycle: evm's `evm-core`
`delegation.rs` test module had been broken since an `Option`→`Result`
API refactor, and a `--tests`-less check let it ride along undetected
from one stable branch to the next. (Since fixed upstream:
rust-ethereum/evm#405.)

---------

Co-authored-by: Rodrigo Quelhas <22591718+RomarQ@users.noreply.github.com>

Author: manuelmauro

moonbeam-engineering/skills/qa-cherry-picks/verify-cherry-picks.md

@@ -20,3 +20,15 @@ Upstream remotes by repo:
 | moonkit      | moonbeam-foundation/moonkit (origin) | Moonsong-Labs/moonkit (branch: `main`)               |
 
 Then for each "Included" row, confirm the commit exists on the branch. For each "Dropped" row, confirm it does not.
+
+## Verify the branch compiles
+
+After confirming the cherry-picks are present, check that the fork branch still
+builds — **including test code**:
+
+```bash
+cargo check --workspace --tests
+```
+
+Always pass `--tests`. Plain `cargo check --workspace` skips `#[cfg(test)]`
+modules and integration tests.