chore: re-enable tracing env-filter feature

The `sn_testnet` crate still requires this feature or it won't compile.

The release commit that bumped the versions after this change was reverted because the `sn_testnet`
crate couldn't be published. This is the first crate in the chain, so we can just revert the whole
release commit and the next time we merge we will get a version bump without the `sn_testnet`
change.

sn_testnet/Cargo.toml

@@ -32,7 +32,7 @@ regex = "1.7.1"
 tonic = { version = "~0.8.3", optional = true }
 tracing = "~0.1.26"
 tracing-core = "~0.1.21"
-tracing-subscriber = { version = "~0.3.1", features = ["json"] }
+tracing-subscriber = { version = "~0.3.1", features = ["env-filter", "json"] }
 xor_name = { version = "~5.0.0", optional = true }
 walkdir = "2"