Runtime: Rebars: Get old rebar binaries when testing old erlang versions

.github/workflows/runtime.yml

@@ -44,6 +44,16 @@ jobs:
 
     - uses: actions/checkout@v4
 
+    - name: Get compatible Rebar binaries
+      if: matrix.otp < 23
+      run: |
+        rm rebar
+        rm rebar3
+        wget https://github.com/processone/ejabberd/raw/21.12/rebar
+        wget https://github.com/processone/ejabberd/raw/21.12/rebar3
+        chmod +x rebar
+        chmod +x rebar3
+
     - name: Prepare libraries
       run: |
         apt-get -qq update