Add OTP 28 to CI test matrix

Author: warmwaffles

.github/workflows/ci.yml

@@ -18,7 +18,7 @@ jobs:
       matrix:
         os: ["ubuntu-latest"]
         elixir: ["1.17"]
-        otp: ["27"]
+        otp: ["28"]
     steps:
       - uses: actions/checkout@v4
       - uses: erlef/setup-beam@v1
@@ -49,7 +49,7 @@ jobs:
       matrix:
         os: ["ubuntu-latest"]
         elixir: ["1.17", "1.16", "1.15"]
-        otp: ["27", "26", "25"]
+        otp: ["28", "27", "26", "25"]
         exclude:
           - elixir: "1.15"
             otp: "27"