Merge bitcoin/bitcoin#32623: test: Add missing ipc subtree to lint

fa4b8b16c3 test: Add missing ipc subtree to lint (MarcoFalke)

Pull request description:

  The subtree docs and lint checks list the subtrees in three places, making it hard to follow and update and easy to miss one.

  Fix all issues by including the missing one and removing the list in one place.

ACKs for top commit:
  l0rinc:
    ACK fa4b8b16c3
  davidgumberg:
    ACK https://github.com/bitcoin/bitcoin/pull/32623/commits/fa4b8b16c37830bf7ee1419aae94e99f294f0e9f
  achow101:
    ACK fa4b8b16c3
  hebasto:
    re-ACK fa4b8b16c3, only a [comment](https://github.com/bitcoin/bitcoin/pull/32623#discussion_r2109243775) has been addressed since my recent [review](https://github.com/bitcoin/bitcoin/pull/32623#pullrequestreview-2871162934).
  BrandonOdiwuor:
    Re-ACK fa4b8b16c3

Tree-SHA512: 97a39cf63be2707b2e03502546797ef639a611030e0a860618256c7c0683381be0f05c8bf850f9542a25266a52f58cef690abf9cc243498b6e026c7a6f9a52b2

test/lint/README.md

@@ -92,11 +92,14 @@ Usage: test/lint/git-subtree-check.sh [-r] DIR [COMMIT]
 
 To do a full check with `-r`, make sure that you have fetched the upstream repository branch in which the subtree is
 maintained:
-* for `src/secp256k1`: https://github.com/bitcoin-core/secp256k1.git (branch master)
-* for `src/leveldb`: https://github.com/bitcoin-core/leveldb-subtree.git (branch bitcoin-fork)
-* for `src/crypto/ctaes`: https://github.com/bitcoin-core/ctaes.git (branch master)
 * for `src/crc32c`: https://github.com/bitcoin-core/crc32c-subtree.git (branch bitcoin-fork)
+* for `src/crypto/ctaes`: https://github.com/bitcoin-core/ctaes.git (branch master)
+* for `src/ipc/libmultiprocess`: https://github.com/bitcoin-core/libmultiprocess (branch master)
+* for `src/leveldb`: https://github.com/bitcoin-core/leveldb-subtree.git (branch bitcoin-fork)
 * for `src/minisketch`: https://github.com/bitcoin-core/minisketch.git (branch master)
+* for `src/secp256k1`: https://github.com/bitcoin-core/secp256k1.git (branch master)
+
+Keep this list in sync with `fn get_subtrees()` in the lint runner.
 
 To do so, add the upstream repository as remote:
 

test/lint/test_runner/src/main.rs

@@ -205,9 +205,11 @@ fn commit_range() -> String {
 
 /// Return all subtree paths
 fn get_subtrees() -> Vec<&'static str> {
+    // Keep in sync with [test/lint/README.md#git-subtree-checksh]
     vec![
         "src/crc32c",
         "src/crypto/ctaes",
+        "src/ipc/libmultiprocess",
         "src/leveldb",
         "src/minisketch",
         "src/secp256k1",