CI: Use checkout v3 for erlang < 20.3, and v4 for newer ones

actions/checkout@v4 updated from node16 to node20,
which requires a recent GLIBC 2.27 or 2.28,
however some old erlang container images include too old GLIBC

.github/workflows/ci.yml

@@ -15,6 +15,9 @@ jobs:
       image: erlang:${{ matrix.otp }}
     steps:
     - uses: actions/checkout@v3
+      if: matrix.otp < '20.3'
+    - uses: actions/checkout@v4
+      if: matrix.otp >= '20.3'
     - run: sed -i 's|applications, \[|applications, \[erl_tidy, |g' src/xmpp.app.src
       if: matrix.otp >= '26'
     - run: make