.gitignore: ignore rustc long type txt files

.gitignore: ignore rustc long type txt files

When rustc prints an error containing a long type that doesn't fit in a
line, it will write the whole thing in a .txt file and print messages
like:

  note: the full type name has been written to
  'path/to/subsystem/module_name.long-type-11621316855315349594.txt'

[ Depending on the compiler version and the kind of error, there are
  two possible spellings -- copying them here for reference:

      = note: the full name for the type has been written to '...long-type-...txt'
      = note: the full type name has been written to '...long-type-...txt'

  In addition, we could clean the files as well in one of our
  cleaning Make targets [1][2].

  Another option would be `--verbose` (but it implies more things
  that we probably don't want) or `-Zwrite-long-types-to-disk=no`
  (unstable so far, but a possible alternative if we prefer to
  avoid the files and simply see the long types in the output
  -- I asked upstream Rust about it [3]).

Link: https://lore.kernel.org/rust-for-linux/CANiq72=cKXdmxEacuGET8fuz_v5eFGB50vnOnKZZJd6iEeAAFA@mail.gmail.com/
Link: https://github.com/Rust-for-Linux/linux/issues/1236
Link: https://rust-lang.zulipchat.com/#narrow/channel/131828-t-compiler/topic/.60-Zwrite-long-types-to-disk.3Dno.60/near/598310194
    - Miguel ]

Long types like core::result::Result<core::pin::Pin<Box<_, Kmalloc,
kernel::error::Error>: pin_init::PinInit<Box<_, Kmalloc>, _> are common
during development, so add a gitignore entry.

Signed-off-by: Manos Pitsidianakis <manos@pitsidianak.is>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Link: https://patch.msgid.link/20260521-rust-gitignore-long-types-txt-v1-1-5be5e6fa427c@pitsidianak.is
[ Moved the lines closer to the existing rust-analyzer one. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>