Update is-macro to 0.1.9

Rust 1.53 introduced an intentional breaking change in attribute
handling in macros, and it led to `is-macro` incorrectly generating code
for `errors::HttpsWebhook::Tls`
(investigated in [rust-lang/rust#85692]). A fix for that landed in
`is-macro` 0.1.9 via [kdy1/is-macro#8], so `tbot` needs to require
`is-macro` to be of version `^0.1.9`.

[rust-lang/rust#85692]: rust-lang/rust#85692
[kdy1/is-macro#8]: kdy1/is-macro#8

Cargo.toml

@@ -34,7 +34,7 @@ native-tls = { version = "0.2", optional = true }
 hyper-rustls = { version = "0.22", optional = true }
 tokio-rustls = { version = "0.22", optional = true }
 hyper-socks2 = { version = "0.6", default-features = false }
-is-macro = "0.1.8"
+is-macro = "0.1.9"
 tracing = "0.1"
 tracing-futures = "0.2"
 type-map = "0.5"