fix(lock): warning suggests non-existent --no-frozen flag (#19290)

[ChrisJr404]

Summary

When uv lock is invoked with UV_FROZEN=1 (env) or frozen set via workspace configuration, the post-success warning suggested using --no-frozen, which does not exist as a CLI flag. Following that hint produces:

$ UV_FROZEN=1 uv lock --no-frozen
error: unexpected argument '--no-frozen' found

  tip: a similar argument exists: '--frozen'

Drop the bad suggestion and recommend --check only, matching the sibling warning emitted when --frozen is passed on the CLI (introduced in #17859).

Old vs new warning

Before:

warning: The lockfile at `uv.lock` was only checked for validity, not whether it is up-to-date, because `UV_FROZEN=1` was provided; use `--no-frozen` or `--check` instead

After:

warning: The lockfile at `uv.lock` was only checked for validity, not whether it is up-to-date, because `UV_FROZEN=1` was provided; use `--check` instead

--check is defined on LockArgs in crates/uv-cli/src/lib.rs (the public, non-hidden flag for "check if the lockfile is up-to-date") and works regardless of whether frozen was set via env, configuration, or the CLI.

Changes

• crates/uv/src/commands/project/lock.rs: drop --no-frozen from the env/configuration warning text.
• crates/uv/tests/it/lock.rs: update the lock_frozen_warning snapshot to match.

Test plan

• cargo build -p uv
• cargo fmt --check
• cargo clippy -p uv --all-targets -- -D warnings
• cargo test -p uv --test it lock::lock_frozen_warning

Closes #19290