devel/gitui: Unbreak build with Rust 1.57.0 (D33190)

error: field is never read: `hash`
  --> asyncgit/src/blame.rs:28:5
   |
28 |     hash: u64,
   |     ^^^^^^^^^
   |

note: the lint level is defined here
  --> asyncgit/src/lib.rs:7:5
   |
7  |     dead_code,
   |     ^^^^^^^^^

error: field is never read: `hash`
  --> asyncgit/src/diff.rs:41:5
   |
41 |     hash: u64,
   |     ^^^^^^^^^

error: field is never read: `request`
  --> asyncgit/src/fetch.rs:28:5
   |
28 |     request: FetchRequest,
   |     ^^^^^^^^^^^^^^^^^^^^^

error: field is never read: `request`
  --> asyncgit/src/push.rs:30:5
   |
30 |     request: PushRequest,
   |     ^^^^^^^^^^^^^^^^^^^^

error: field is never read: `request`
  --> asyncgit/src/push_tags.rs:26:5
   |
26 |     request: PushTagsRequest,
   |     ^^^^^^^^^^^^^^^^^^^^^^^^

error: could not compile `asyncgit` due to 5 previous errors

http://package22.nyi.freebsd.org/data/130amd64-default-foo/2021-12-02_10h34m54s/logs/errors/gitui-0.16.2_3.log

PR:		260140

devel/gitui/Makefile

@@ -186,6 +186,7 @@ CARGO_CRATES=	addr2line-0.15.2 \
 		winapi-x86_64-pc-windows-gnu-0.4.0 \
 		xml-rs-0.8.3 \
 		yaml-rust-0.4.5
+RUSTFLAGS+=	--cap-lints=warn
 PLIST_FILES=	bin/${PORTNAME}
 
 BINARY_ALIAS=	python3=${PYTHON_CMD} # xcb requires python3