Move serde_json_test crate to own workspace

Fixes the following error when testing against a compiler older
than 1.64:

    error: failed to select a version for the requirement `hashbrown = "^0.14"`
    candidate versions found which didn't match: 0.13.2, 0.13.1, 0.12.3, ...
    location searched: crates.io index
    required by package `indexmap v2.0.0`
        ... which satisfies dependency `indexmap = "^2"` of package `serde_json v1.0.97`
        ... which satisfies path dependency `serde_json` of package `serde_json_test v0.0.0`

.github/workflows/ci.yml

@@ -121,5 +121,5 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - uses: dtolnay/install@cargo-outdated
-      - run: cargo outdated --workspace --exit-code 1
+      - run: cargo outdated --exit-code 1
       - run: cargo outdated --manifest-path fuzz/Cargo.toml --exit-code 1

Cargo.toml

@@ -28,9 +28,6 @@ serde_derive = "1.0"
 serde_stacker = "0.1"
 trybuild = { version = "1.0.49", features = ["diff"] }
 
-[workspace]
-members = ["tests/crate"]
-
 [lib]
 doc-scrape-examples = false
 

fuzz/Cargo.toml

@@ -17,5 +17,3 @@ name = "from_slice"
 path = "fuzz_targets/from_slice.rs"
 test = false
 doc = false
-
-[workspace]

tests/crate/Cargo.toml

@@ -15,7 +15,7 @@ serde_json = { path = "../..", default-features = false }
 default = ["std"]
 std = ["serde_json/std"]
 alloc = ["serde_json/alloc"]
-preserve_order = ["serde_json/preserve_order"]
+#preserve_order = ["serde_json/preserve_order"]
 arbitrary_precision = ["serde_json/arbitrary_precision"]
 raw_value = ["serde_json/raw_value"]
 unbounded_depth = ["serde_json/unbounded_depth"]