ci: silence unnecessary_map_or lint as solution requires MSRV >= 1.70

Rust 1.84.0 was recently released along with some new clippy lints, one
of which is `unnecessary_map_or`. Unfortunately this lint suggests using
`Option::is_some_and` as a fix, but this is only available in Rust
 version >= 1.70, while we still have an MSRV of 1.63. So we silence that
lint for now.

We'd still like our lint CI to use stable Rust so that we can benefit from
new lint checks which may be helpful and don't require an MSRV bump, but
sometimes new lints (like in this case) do.

See:
  https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_map_or
  https://doc.rust-lang.org/std/option/enum.Option.html#method.is_some_and

ci/check-lint.sh

@@ -93,4 +93,5 @@ RUSTFLAGS='-D warnings' cargo clippy -- \
 	-A clippy::unnecessary_to_owned \
 	-A clippy::unnecessary_unwrap \
 	-A clippy::unused_unit \
-	-A clippy::useless_conversion
+	-A clippy::useless_conversion \
+	-A clippy::unnecessary_map_or `# to be removed once we hit MSRV 1.70`