build: explicitly set publish = false for internal crates (apache#21869)

## Which issue does this PR close?

N/A

## Rationale for this change

this is done so we can query cargo metadata alone to find only user
facing crates
and to use cargo metadata to find user facing crates when searching for
breaking changes in pr as suggested here:
-
apache#21499 (comment)

## What changes are included in this PR?
set `publish = false` for:
1. `datafusion-benchmarks`
2. `datafusion-wasmtest`
3. `test-utils`

## Are these changes tested?

I verified that these are not already published to crates.io and not in
`dev/release/README.md` _Publish on Crates.io_ list

## Are there any user-facing changes?

No

Author: rluvaton

benchmarks/Cargo.toml

@@ -25,6 +25,7 @@ homepage = { workspace = true }
 repository = { workspace = true }
 license = { workspace = true }
 rust-version = { workspace = true }
+publish = false
 
 # Note: add additional linter rules in lib.rs.
 # Rust does not support workspace + new linter rules in subcrates yet

datafusion/wasmtest/Cargo.toml

@@ -26,6 +26,7 @@ repository = { workspace = true }
 license = { workspace = true }
 authors = { workspace = true }
 rust-version = { workspace = true }
+publish = false
 
 [package.metadata.docs.rs]
 all-features = true

test-utils/Cargo.toml

@@ -19,6 +19,7 @@
 name = "test-utils"
 version = "0.1.0"
 edition = { workspace = true }
+publish = false
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html