Gradle failing to sign build of StreetComplete

The builds of de.westnordost.streetcomplete are alternately failing with the (known: fdroidserver#766 (closed)) could not bring up vm 'builder_default' message, and a new one, wherein Gradle can't sign it.

> Configure project :app
e: /home/vagrant/build/de.westnordost.streetcomplete/app/build.gradle.kts:65:5: Unresolved reference: releaseSigningConfig
e: /home/vagrant/build/de.westnordost.streetcomplete/app/build.gradle.kts:66:5: Unresolved reference: releaseSigningConfig
e: /home/vagrant/build/de.westnordost.streetcomplete/app/build.gradle.kts:67:5: Unresolved reference: releaseSigningConfig
e: /home/vagrant/build/de.westnordost.streetcomplete/app/build.gradle.kts:68:5: Unresolved reference: releaseSigningConfig

FAILURE: Build failed with an exception.

* Where:
Build file '/home/vagrant/build/de.westnordost.streetcomplete/app/build.gradle.kts' line: 65

* What went wrong:
Script compilation errors:

  Line 65:     releaseSigningConfig.storeFile = file(props.getProperty("storeFile"))
               ^ Unresolved reference: releaseSigningConfig

  Line 66:     releaseSigningConfig.storePassword = props.getProperty("storePassword")
               ^ Unresolved reference: releaseSigningConfig

  Line 67:     releaseSigningConfig.keyAlias = props.getProperty("keyAlias")
               ^ Unresolved reference: releaseSigningConfig

  Line 68:     releaseSigningConfig.keyPassword = props.getProperty("keyPassword")
               ^ Unresolved reference: releaseSigningConfig

4 errors