use different rebar versions

.github/workflows/test.yml

@@ -13,13 +13,16 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        otp_version:
-        - "25.x"
-        - "24.x"
-        - "23.x"
-        - "22.x"
-        - "21.x"
-        - "20.x"
+        include:
+        - otp_version: "25.x"
+        - otp_version: "24.x"
+        - otp_version: "23.x"
+        - otp_version: "22.x"
+          rebar3-version: 3.6.1
+        - otp_version: "21.x"
+          rebar3-version: 3.6.1
+        - otp_version: "20.x"
+          rebar3-version: 3.6.1
         os: [ubuntu-latest]
     env:
       OTP_VERSION: ${{ matrix.otp_version }}
@@ -28,6 +31,7 @@ jobs:
       - uses: erlef/setup-beam@v1
         with:
           otp-version: ${{ matrix.otp_version }}
+          rebar3-version: ${{ matrix.rebar3-version }}
       - uses: actions/cache@v2
         name: Cache
         with: