ci: pin nimble 0.22.3 to fix Nim checksum mismatch on liblogosdelivery build

The "Build liblogosdelivery.so" job ran a bare `nimble install -y` inside
the logos-delivery checkout, resolving the package's locked deps with
whatever nimble choosenim ships. That nimble recomputes the locked Nim
package checksum differently from the nimble that generated nimble.lock
(0.22.3), so the build aborted with:

  Downloaded package checksum does not correspond to that in the lock file:
    Package:           nim@v.2.2.4@r.911e0dbb...
    Expected checksum: 68bb85cb...

Mirror logos-delivery's own CI: pin nimble 0.22.3 after installing Nim, and
drop the redundant `nimble install -y` / no-op `make setup`. `make
liblogosdelivery` already resolves the locked deps via its build-deps
prerequisite (`nimble setup --localdeps`).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.github/workflows/pr_tests.yml

@@ -71,7 +71,7 @@ jobs:
             gcc \
             g++
 
-      - name: Install Nim 2.2.4
+      - name: Install Nim 2.2.4 and Nimble 0.22.3
         if: steps.cache-lib.outputs.cache-hit != 'true'
         run: |
           set -euo pipefail
@@ -79,6 +79,10 @@ jobs:
           echo "$HOME/.nimble/bin" >> "$GITHUB_PATH"
           export PATH="$HOME/.nimble/bin:$PATH"
           choosenim 2.2.4
+          # Pin the nimble that generated logos-delivery's nimble.lock. A newer
+          # nimble recomputes the locked Nim package checksum differently, which
+          # makes `nimble setup --localdeps` abort with a checksum mismatch.
+          (cd /tmp && nimble install "nimble@0.22.3" -y)
           nim --version
           nimble --version
 
@@ -98,10 +102,10 @@ jobs:
 
           ln -sf waku.nimble waku.nims
 
-          nimble install -y
-
-          make setup
-
+          # `make liblogosdelivery` resolves the locked deps via
+          # `nimble setup --localdeps` (build-deps prerequisite); a bare
+          # `nimble install -y` here is redundant and pulls Nim from the lock,
+          # which is what triggered the checksum mismatch.
           make liblogosdelivery
 
           SO_PATH="$(find . -type f -name 'liblogosdelivery.so' | head -n 1)"