chore: skip nexus-staging-maven-plugin for central portal migration

[mpeddada1]

Verified with mvn clean deploy -V -DaltDeploymentRepository=local::default::file:${local_staging_dir} -DskipTests=true -P=-release-sonatype -P=-release-staging-repository -P=-clirr-compatibility-check -P=-checkstyle-tests -P=-animal-sniffer:

[INFO] Installing /usr/local/google/home/mpeddada/IdeaProjects/cloud-spanner-r2dbc/cloud-spanner-r2dbc/pom.xml to /usr/local/google/home/mpeddada/.m2/repository/com/google/cloud/cloud-spanner-r2dbc/1.4.1/cloud-spanner-r2dbc-1.4.1.pom
[INFO] 
[INFO] --- maven-deploy-plugin:3.1.1:deploy (default-deploy) @ cloud-spanner-r2dbc ---
[INFO] Using alternate deployment repository local::default::file:/tmp/maven-staging-dir.rK6dRI
[WARNING] Using legacy syntax for alternative repository. Use "local::file:/tmp/maven-staging-dir.rK6dRI" instead.
Uploading to local: file:/tmp/maven-staging-dir.rK6dRI/com/google/cloud/cloud-spanner-r2dbc/1.4.1/cloud-spanner-r2dbc-1.4.1.pom
Uploaded to local: file:/tmp/maven-staging-dir.rK6dRI/com/google/cloud/cloud-spanner-r2dbc/1.4.1/cloud-spanner-r2dbc-1.4.1.pom (4.5 kB at 497 kB/s)
Uploading to local: file:/tmp/maven-staging-dir.rK6dRI/com/google/cloud/cloud-spanner-r2dbc/1.4.1/cloud-spanner-r2dbc-1.4.1.jar
Uploaded to local: file:/tmp/maven-staging-dir.rK6dRI/com/google/cloud/cloud-spanner-r2dbc/1.4.1/cloud-spanner-r2dbc-1.4.1.jar (83 kB at 10 MB/s)
Downloading from local: file:/tmp/maven-staging-dir.rK6dRI/com/google/cloud/cloud-spanner-r2dbc/maven-metadata.xml
Downloaded from local: file:/tmp/maven-staging-dir.rK6dRI/com/google/cloud/cloud-spanner-r2dbc/maven-metadata.xml (315 B at 29 kB/s)
Uploading to local: file:/tmp/maven-staging-dir.rK6dRI/com/google/cloud/cloud-spanner-r2dbc/maven-metadata.xml
Uploaded to local: file:/tmp/maven-staging-dir.rK6dRI/com/google/cloud/cloud-spanner-r2dbc/maven-metadata.xml (315 B at 315 kB/s)

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud