Make gemini ignore `Lib/**` (#5903) #14494

Job	Run time
Ensure compilation on various targets	42s
Run rust tests (macos-latest)	26s
Run rust tests (ubuntu-latest)	40s
Check Rust code with rustfmt and clippy	40s
Run tests under miri	41s
Run snippets and cpython tests (macos-latest)	27s
Check the WASM package and demo	25s
Run rust tests (windows-latest)	29s
Run snippets and cpython tests on wasm-wasi	40s
Run snippets and cpython tests (windows-latest)	32s
Run snippets and cpython tests (ubuntu-latest)	1s
	5m 43s

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