alpine: update clang19-dev/llvm19 to clang20-dev/llvm20

[abetomo]

The PostgreSQL base image has changed.
docker-library/postgres@b6a26b9

[Copilot]

Pull request overview

Updates Alpine-based PostgreSQL extension images to match the newer toolchain required by the upstream postgres:* -alpine base image change referenced in the PR description.

Changes:

• Bump build dependency clang19-dev → clang20-dev across all Alpine image variants.
• Bump build dependency llvm19 → llvm20 across all Alpine image variants.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
alpine/14/Dockerfile	Updates Alpine build deps to clang/llvm 20 for Postgres 14 image builds.
alpine/14-slim/Dockerfile	Same clang/llvm 20 bump for the Postgres 14 slim variant.
alpine/15/Dockerfile	Updates Alpine build deps to clang/llvm 20 for Postgres 15 image builds.
alpine/15-slim/Dockerfile	Same clang/llvm 20 bump for the Postgres 15 slim variant.
alpine/16/Dockerfile	Updates Alpine build deps to clang/llvm 20 for Postgres 16 image builds.
alpine/16-slim/Dockerfile	Same clang/llvm 20 bump for the Postgres 16 slim variant.
alpine/17/Dockerfile	Updates Alpine build deps to clang/llvm 20 for Postgres 17 image builds.
alpine/17-slim/Dockerfile	Same clang/llvm 20 bump for the Postgres 17 slim variant.
alpine/18/Dockerfile	Updates Alpine build deps to clang/llvm 20 for Postgres 18 image builds.
alpine/18-slim/Dockerfile	Same clang/llvm 20 bump for the Postgres 18 slim variant.

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