aya-bpf-macros: fix tests

Doctests were failing due to a dependency on the aya-bpf crate.

bpf/aya-bpf-macros/Cargo.toml

@@ -10,4 +10,7 @@ proc-macro = true
 [dependencies]
 proc-macro2 = "1.0"
 quote = "1.0"
-syn = {version = "1.0", features = ["full"]}
+syn = {version = "1.0", features = ["full"]}
+
+[dev-dependencies]
+aya-bpf = { path = "../aya-bpf" }