Switch to released OTP/Elixir versions on CI

Previously, we tried using the latest version of both Elixir and
OTP. Since we're having trouble with hex.pm currently, switch to
released versions of both to decrease the reliance on hex.pm.

.github/workflows/ci.yaml

@@ -21,8 +21,8 @@ jobs:
       - name: Set up Erlang and Elixir
         uses: erlef/setup-beam@v1
         with:
-          otp-version: latest
-          elixir-version: latest
+          otp-version: 27.x
+          elixir-version: 1.17.x
       - name: Checkout code
         uses: actions/checkout@v4
       - name: Check code formatting
@@ -34,8 +34,8 @@ jobs:
       - name: Set up Erlang and Elixir
         uses: erlef/setup-beam@v1
         with:
-          otp-version: latest
-          elixir-version: latest
+          otp-version: 27.x
+          elixir-version: 1.17.x
       - name: Checkout code
         uses: actions/checkout@v4
       - name: Get dependencies
@@ -49,8 +49,8 @@ jobs:
       - name: Set up Erlang and Elixir
         uses: erlef/setup-beam@v1
         with:
-          otp-version: latest
-          elixir-version: latest
+          otp-version: 27.x
+          elixir-version: 1.17.x
       - name: Checkout code
         uses: actions/checkout@v4
       - name: Get dependencies
@@ -87,8 +87,8 @@ jobs:
       - name: Set up Erlang and Elixir
         uses: erlef/setup-beam@v1
         with:
-          otp-version: latest
-          elixir-version: latest
+          otp-version: 27.x
+          elixir-version: 1.17.x
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with:
@@ -109,8 +109,8 @@ jobs:
       - name: Set up Erlang and Elixir
         uses: erlef/setup-beam@v1
         with:
-          otp-version: latest
-          elixir-version: latest
+          otp-version: 27.x
+          elixir-version: 1.17.x
       - name: Checkout code
         uses: actions/checkout@v4
       - name: Get dependencies