ios: sign with disposable login keychain

.gitea/workflows/testflight-release.yml

@@ -91,7 +91,7 @@ jobs:
           developer_dir="$(xcode-select -p)"
           signing_dir="$(mktemp -d "${RUNNER_TEMP:-${TMPDIR:-/tmp}}/sybil-signing.XXXXXX")"
           mkdir -p "${HOME}/Library/Keychains"
-          keychain_name="${HOME}/Library/Keychains/${SIGNING_KEYCHAIN}-${GITHUB_RUN_ID:-$(uuidgen)}.keychain"
+          keychain_name="${HOME}/Library/Keychains/login.keychain"
           certificate_path="${signing_dir}/appstore-signing.p12"
           wwdr_certificate_path="${signing_dir}/AppleWWDRCAG3.cer"
           profile_path="${signing_dir}/Sybil_AppStore_CI.mobileprovision"

ios/fastlane/CI.md

@@ -13,14 +13,15 @@ git tag release/v1.10.0
 git push origin release/v1.10.0
 ```
 
-The release job runs on the `xcode` runner label, imports the signing p12 into
+The release job runs on the `xcode` runner label, creates the runner user's
-a temporary per-user keychain, makes that keychain the user default for the
+login keychain from Gitea secrets, makes that keychain the user default for the
 duration of the job, installs the App Store provisioning profile in both the
 legacy MobileDevice directory and the Xcode UserData directory used by newer
 Xcode releases, builds and uploads the app with fastlane, then creates or
 updates the matching Gitea release with the generated IPA as an asset. The job
-restores the previous user default keychain and deletes the temporary signing
+restores the previous user default keychain and deletes the user login keychain
-keychain and installed profiles in an `always()` cleanup step.
+and installed profiles in an `always()` cleanup step. No signing material is
+installed into the system keychain.
 
 Required repository secrets: