Rollup merge of #69047 - ehuss:rustfmt-vendor, r=Centril
Rollup merge of #69047 - ehuss:rustfmt-vendor, r=Centril

Don't rustfmt check the vendor directory.

I need to be able to run `x.py tidy` to do license checks (which requires vendored dependencies).  However, when vendoring is enabled, it wants to rustfmt check the entire vendor directory, which doesn't work.

aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust