🔨 zv: Don't enable gvariant feature for dbus fuzz target

Otherwise, it can enable Maybe singature support, which will fail with an
assertion when used with dbus ser/de.

.github/workflows/rust.yml

@@ -219,7 +219,7 @@ jobs:
         run: |
           cargo --locked install cargo-fuzz
           cargo --locked fuzz run --fuzz-dir zvariant/fuzz dbus -- -max_total_time=30 -max_len=100M
-          cargo --locked fuzz run --fuzz-dir zvariant/fuzz gvariant -- -max_total_time=30 -max_len=100M
+          cargo --locked fuzz run --fuzz-dir zvariant/fuzz --features gvariant gvariant -- -max_total_time=30 -max_len=100M
 
   doc_build:
     runs-on: ubuntu-latest

zvariant/fuzz/Cargo.toml

@@ -7,13 +7,18 @@ edition = "2021"
 [package.metadata]
 cargo-fuzz = true
 
+[features]
+# `gvariant` is only needed for the `gvariant` fuzz target. However, we don't want it to
+# be enabled for running the `dbus` fuzz target, as that can cause certain assertions to fail.
+# FIXME: Is there a better way to do this?
+gvariant = ["zvariant/gvariant"]
+
 [dependencies]
 libfuzzer-sys = "0.4.7"
 endi = "1.1.0"
 
 [dependencies.zvariant]
 path = ".."
-features = ["gvariant"]
 
 # Prevent this from interfering with workspaces
 [workspace]