Use setup-nim-action V2

Fix

Author: juancarlospaco

.github/workflows/selftesting.yml

@@ -7,10 +7,10 @@ jobs:
   test:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
-    - uses: jiro4989/setup-nim-action@v1
+    - uses: actions/checkout@v5
+    - uses: jiro4989/setup-nim-action@v2
       with:
-        nim-version: 'devel'
+        nim-version: 'stable'
     - name: Install Dependencies
       run: sudo apt-get install --no-install-recommends -yq valgrind
     - uses: ./