Update to ostree-ext 0.6

Part of general crate updates.

tests/inst/Cargo.toml

@@ -17,7 +17,7 @@ serde_json = "1.0"
 sh-inline = "0.1.0"
 anyhow = "1.0"
 tempfile = "3.1.0"
-ostree-ext = { version = "0.3.0" }
+ostree-ext = { version = "0.6.0" }
 libtest-mimic = "0.3.0"
 twoway = "0.2.1"
 hyper = { version = "0.14", features = ["runtime", "http1", "http2", "tcp", "server"] }