Work around Cargo Issue 10788

See rust-lang/cargo#10788 for the full issue.

When enabling a feature of a dependency, the syntax `tokio/rt` implicitly required a feature `tokio` to exist in 1.70 of cargo. By 1.77 this has been fixed. To work around this, we can use "weak feature dependencies" like `tokio?/rt` which enables the `rt` feature of tokio only if tokio is itself an enabled dependency. Also adding `dep:tokio` to the list of dependencies ensures that this is always true.

When the MSRV is upgraded again, we can probably remove the weak `?` and the `dep:tokio` in these cases.

tonic/Cargo.toml

@@ -33,8 +33,9 @@ tls = [
   "transport",
   "dep:tokio-rustls",
   "dep:rustls",
-  "tokio/rt",
-  "tokio/macros",
+  "dep:tokio",
+  "tokio?/rt",
+  "tokio?/macros",
 ]
 tls-roots = ["tls-roots-common", "dep:rustls-native-certs"]
 tls-roots-common = ["tls"]