Rollup merge of #102846 - zertosh:update-syn, r=dtolnay

update to syn-1.0.102

This update removes the only `.gitignore` found in `rustc-src`:

    vendor/syn/tests/.gitignore
    vendor/syn-1.0.91/tests/.gitignore
    vendor/syn-1.0.95/tests/.gitignore

To check-in `rustc-src` for hermetic builds in environments with
restrictive `.gitignore` policies, one has to remove these
`tests/.gitignore` and patch the respective
`.cargo-checksum.json`.`syn` >1.0.101 includes dtolnay/syn@3c49303bed7a,
which removes its `tests/.gitignore`. Now the `syn` crates.io package
has no `.gitignore`.

[`rustc-src`'s `vendor`][] is produced from the root `Cargo.toml`,
`src/tools/rust-analyzer/Cargo.toml`,
`compiler/rustc_codegen_cranelift/Cargo.toml`, and
`src/bootstrap/Cargo.toml`. `rustc_codegen_cranelift` does not use
`syn`.

[`rustc-src`'s `vendor`]:
  https://github.com/rust-lang/rust/blob/c0784109daa0/src/bootstrap/dist.rs#L934-L940

This was produced with:

    cargo update --package syn --precise 1.0.102 \

    cargo update --package syn --precise 1.0.102 \
        --manifest-path src/tools/rust-analyzer/Cargo.toml

    cargo update --package syn --precise 1.0.102 \
        --manifest-path src/bootstrap/Cargo.toml

Author: matthiaskrgr