fix(ci): remove ref specification in checkout step (#127)

Signed-off-by: Jan-Hendrik Spahn <jan-hendrik.spahn@soptim.de>

Author: spah-soptim

.github/workflows/backend-ci.yml

@@ -24,7 +24,6 @@ jobs:
       - name: Checkout
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
         with:
-          ref: ${{ github.head_ref || github.ref }}
           fetch-depth: 0
           submodules: true
       - name: Setup Java

.github/workflows/frontend-ci.yml

@@ -24,7 +24,6 @@ jobs:
       - name: Checkout
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
         with:
-          ref: ${{ github.head_ref || github.ref }}
           fetch-depth: 0
       - name: Setup Node.js
         uses: actions/setup-node@53b83947a5a98c8d113130e565377fae1a50d02f # v6.3.0