ci: keep Elixir/OTP versions in every deps cache key

The 1.19/OTP 26 matrix entry and the coverage job share no prefix: each
restores only caches built by the same toolchain, so cover can always
re-instrument the beams.

Author: gilbertwong96

.github/workflows/ci.yml

@@ -32,8 +32,8 @@ jobs:
           path: |
             deps
             _build
-          key: ${{ runner.os }}-mix-1.20-27-${{ hashFiles('**/mix.lock') }}
-          restore-keys: ${{ runner.os }}-mix-
+          key: ${{ runner.os }}-mix-${{ matrix.elixir }}-${{ matrix.otp }}-${{ hashFiles('**/mix.lock') }}
+          restore-keys: ${{ runner.os }}-mix-${{ matrix.elixir }}-${{ matrix.otp }}-
 
       - uses: actions/cache@v4
         with:
@@ -65,7 +65,7 @@ jobs:
             deps
             _build
           key: ${{ runner.os }}-mix-1.20-27-${{ hashFiles('**/mix.lock') }}
-          restore-keys: ${{ runner.os }}-mix-
+          restore-keys: ${{ runner.os }}-mix-1.20-27-
 
       - name: Fetch dependencies
         run: mix deps.get