chore: bump DuckDB to v1.5.5 (keep v1.4 LTS)

[jrosskopf]

Summary

Bumps the duckdb submodule (v1.5.3 -> v1.5.5) and updates
.github/workflows/MainDistributionPipeline.yml accordingly, while
keeping the dual v1.4 LTS / v1.5 stable release matrix intact.

Submodule

• duckdb: v1.5.3 -> v1.5.5

Workflow edits (.github/workflows/MainDistributionPipeline.yml)

• duckdb-stable-build / duckdb-stable-deploy: duckdb_version,
  ci_tools_version, and the uses: ...@v1.5.3 ref all bumped to
  v1.5.5.
• duckdb-lts-build / duckdb-lts-deploy: LTS duckdb_version
  normalized v1.4.4 -> v1.4.5. ci_tools_version and the
  uses: ...@v1.5.3 ref bumped to v1.5.5 (the LTS jobs intentionally
  reuse the stable extension-ci-tools tooling for the MSVC-cl
  Windows fix — see the file's header comment, unchanged).
• Human-readable name:/comment strings referencing the old versions
  (v1.5.3, v1.4.4) updated to match (v1.5.5, v1.4.5).
• No jobs added, removed, or reordered; the v1.4 LTS jobs remain.

No other genuine version pins were found (checked vcpkg.json,
Makefile, CMakeLists.txt/extension_config.cmake for stray
DUCKDB_GIT_VERSION/version literals — none present outside the
workflow file and the submodule pointer).

Local verification on bigfox

• Build: buildStatus=pass — clean GEN=ninja make release build
  (no GCC-16 ODR/link issues this time), producing
  build/release/extension/quack_oauth/quack_oauth.duckdb_extension.
• Tests: testStatus=pass — make test_release: all SQL tests
  passed (168 assertions in 11 test cases, 1 test skipped via
  require quack as expected without the sibling quack extension
  installed).

Test plan

• duckdb submodule pinned to v1.5.5
• GEN=ninja make release builds cleanly, extension artifact present
• make test_release — all SQL tests pass
• CI green on both the duckdb-stable-* (v1.5.5) and
  duckdb-lts-* (v1.4.5) job pairs

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