chore(deps): update actions/cache action to v6 (#922)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/elixir.yml

@@ -52,7 +52,7 @@ jobs:
           elixir-version: ${{ matrix.elixir }}
           otp-version: ${{ matrix.otp }}
       - name: Retrieve Mix Dependencies Cache
-        uses: actions/cache@v5
+        uses: actions/cache@v6
         id: mix-cache # id to use in retrieve action
         with:
           path: deps
@@ -103,13 +103,13 @@ jobs:
           elixir-version: ${{ matrix.elixir }}
           otp-version: ${{ matrix.otp }}
       - name: Retrieve Mix Dependencies Cache
-        uses: actions/cache@v5
+        uses: actions/cache@v6
         id: mix-cache # id to use in retrieve action
         with:
           path: deps
           key: ${{ runner.os }}-${{ matrix.otp }}-${{ matrix.elixir }}-mix-${{ hashFiles('mix.lock') }}
       - name: Retrieve PLT Cache
-        uses: actions/cache@v5
+        uses: actions/cache@v6
         id: plt-cache
         with:
           path: priv/plts