Move signing.secretKeyRingFile from gradle.properties into build.gradle

This allows correctly setting it to an absolute path based on the
project directory. The location of the secret key ring is not sensitive
information, so it does not need to be stored encrypted.

build.gradle

@@ -8,6 +8,8 @@ allprojects {
   project.group = 'de.hhu.stups'
   project.version = '3.3.0-SNAPSHOT'
   project.ext.isSnapshot = project.version.endsWith("-SNAPSHOT")
+
+  ext."signing.secretKeyRingFile" = file("secring.gpg").absolutePath
 }
 
 wrapper {

gradle.properties.enc

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-oypMpm9HRBMEZyDkPRPJ2DKOFhW6YCdcszCjTNKmeJkOwVjfyltC43WXzcrzYKR/
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-qjWQ8xnLXRorA7j0lkWAhw==
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