fix: import GPG signing key for Maven signing in ci-build

The maven-gpg-plugin signs via the local gpg keyring, but secring.gpg
was downloaded and copied without ever being imported, leaving the
keyring empty on the fresh build agent. Add a gpg --import step so the
signing key is available, and remove the unused \ variable
left over from the Gradle build.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: ramsessanchez

.azure-pipelines/ci-build.yml

@@ -60,10 +60,15 @@ extends:
                   Copy-Item $(downloadLocalProperties.secureFilePath) local.properties -Verbose
                 displayName: Copy secring and 'local.properties'
 
+              - pwsh: |
+                  # maven-gpg-plugin signs via the local gpg keyring, so the key from
+                  # secring.gpg must be imported into gpg before signing can succeed.
+                  gpg --batch --import secring.gpg
+                displayName: Import GPG signing key
+
               - pwsh: |
                   $props = Get-Content local.properties -Raw
                   $keyId = ($props | Select-String -Pattern 'signing\.keyId=(.+)').Matches.Groups[1].Value
-                  $keyRingFile = ($props | Select-String -Pattern 'signing\.secretKeyRingFile=(.+)').Matches.Groups[1].Value
                   $keyPassword = ($props | Select-String -Pattern 'signing\.password=(.+)').Matches.Groups[1].Value
 
                   $settingsXml = @"