ci: Fix filtering out Qt-generated files from `compile_commands.json` #31928

This PR:

1. Adjusts the regex for Qt-generated files to match the CMake build directory structure.
2. Moves the filtering command to run before clang-tidy, ensuring that Qt-generated files are not needlessly processed.

Fixes #31801.

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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/31928.

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ACK d82dc1041524e8402d201d32c9143233b5ec1baf 🚂

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post-merge ACK d82dc1041524e8402d201d32c9143233b5ec1baf

Verified that the regex adjustment successfully excludes CMake-generated files (bitcoinqt_autogen/), as evidenced by the absence of clang-tidy runs on these files in the updated logs.