Added conditional dependancy downloading in CI

Progresses google#1310

Cargo.toml

@@ -18,13 +18,7 @@ name = "zerocopy"
 version = "0.8.0-alpha.15"
 authors = ["Joshua Liebow-Feeser <joshlf@google.com>"]
 description = "Utilities for zero-copy parsing and serialization"
-categories = [
-  "embedded",
-  "encoding",
-  "no-std::no-alloc",
-  "parsing",
-  "rust-patterns",
-]
+categories = ["embedded", "encoding", "no-std::no-alloc", "parsing", "rust-patterns"]
 keywords = ["cast", "convert", "transmute", "transmutation", "type-punning"]
 license = "BSD-2-Clause OR Apache-2.0 OR MIT"
 repository = "https://github.com/google/zerocopy"
@@ -70,12 +64,7 @@ std = ["alloc"]
 # This feature depends on all other features that work on the stable compiler.
 # We make no stability guarantees about this feature; it may be modified or
 # removed at any time.
-__internal_use_only_features_that_work_on_stable = [
-  "alloc",
-  "derive",
-  "simd",
-  "std",
-]
+__internal_use_only_features_that_work_on_stable = ["alloc", "derive", "simd", "std"]
 
 [dependencies]
 zerocopy-derive = { version = "=0.8.0-alpha.15", path = "zerocopy-derive", optional = true }