Use explicit CI signing keychain

.gitea/workflows/testflight.yml

@@ -33,6 +33,25 @@ jobs:
             brew install xcodegen
           fi
 
+      - name: Prepare Runner Keychain
+        env:
+          HOME: /var/lib/act_runner
+        run: |
+          set -euo pipefail
+          mkdir -p "${HOME}/Library/Keychains"
+
+          login_keychain="${HOME}/Library/Keychains/login.keychain"
+          if [ ! -f "${login_keychain}-db" ]; then
+            security create-keychain -p "" "${login_keychain}"
+          fi
+
+          security unlock-keychain -p "" "${login_keychain}" 2>/dev/null || \
+            security unlock-keychain -p "sybil-ci-keychain-password" "${login_keychain}" 2>/dev/null || true
+          security default-keychain -s "${login_keychain}"
+          security list-keychains -d user -s "${login_keychain}-db"
+          security delete-keychain "${HOME}/Library/Keychains/sybil_ci_keychain" >/dev/null 2>&1 || true
+          rm -f "${HOME}/Library/Keychains/sybil_ci_keychain" "${HOME}/Library/Keychains/sybil_ci_keychain-db"
+
       - name: Upload to TestFlight
         working-directory: ios
         env: