Update to DuckDB v1.5-variegata

- Update MainDistributionPipeline.yml versions to v1.5-variegata

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: rustyconover

.github/workflows/MainDistributionPipeline.yml

@@ -13,8 +13,8 @@ concurrency:
 jobs:
   duckdb-stable-build:
     name: Build extension binaries
-    uses: duckdb/extension-ci-tools/.github/workflows/_extension_distribution.yml@main
+    uses: duckdb/extension-ci-tools/.github/workflows/_extension_distribution.yml@v1.5-variegata
     with:
-      duckdb_version: main
-      ci_tools_version: main
+      duckdb_version: v1.5-variegata
+      ci_tools_version: v1.5-variegata
       extension_name: httpserver