Release workflows: use ASF org-shared Nexus deployer secret names

Nexus staging deploys returned HTTP 401 because the release workflows
read secrets.PARQUET_NEXUS_USER / PARQUET_NEXUS_PASSWORD, which don't
exist on apache/parquet-java. ASF Infra shares the deployer credentials
at the org level under NEXUS_STAGE_DEPLOYER_USER / NEXUS_STAGE_DEPLOYER_PW.
Point the workflows at those names so the env vars are populated and
Nexus accepts the upload.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: RussellSpitzer

.github/workflows/release-prepare-rc.yml

@@ -79,8 +79,8 @@ jobs:
       - name: Prepare Release Candidate
         env:
           DRY_RUN: ${{ inputs.dry_run && '1' || '0' }}
-          NEXUS_USERNAME: ${{ secrets.PARQUET_NEXUS_USER }}
-          NEXUS_PASSWORD: ${{ secrets.PARQUET_NEXUS_PASSWORD }}
+          NEXUS_USERNAME: ${{ secrets.NEXUS_STAGE_DEPLOYER_USER }}
+          NEXUS_PASSWORD: ${{ secrets.NEXUS_STAGE_DEPLOYER_PW }}
           SVN_USERNAME: ${{ secrets.PARQUET_SVN_DEV_USERNAME }}
           SVN_PASSWORD: ${{ secrets.PARQUET_SVN_DEV_PASSWORD }}
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

.github/workflows/release-publish.yml

@@ -82,8 +82,8 @@ jobs:
       - name: Publish Release
         env:
           DRY_RUN: ${{ inputs.dry_run && '1' || '0' }}
-          NEXUS_USERNAME: ${{ secrets.PARQUET_NEXUS_USER }}
-          NEXUS_PASSWORD: ${{ secrets.PARQUET_NEXUS_PASSWORD }}
+          NEXUS_USERNAME: ${{ secrets.NEXUS_STAGE_DEPLOYER_USER }}
+          NEXUS_PASSWORD: ${{ secrets.NEXUS_STAGE_DEPLOYER_PW }}
           SVN_USERNAME: ${{ secrets.PARQUET_SVN_DEV_USERNAME }}
           SVN_PASSWORD: ${{ secrets.PARQUET_SVN_DEV_PASSWORD }}
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}