Actually build gix to check MSRV

This changes `cargo check` commands to `cargo build` in the
`ci-check-msrv` recipe in the `justfile`, which the `check-msrv` CI
jobs in `msrv.yml` use.

The idea is to make sure at least `gix` (with the two combinations
of features tested) actuall *builds* under the MSRV toolchain.

As in f10f18d, this also updates the `Makefile` rule corresponding
to that `justfile` recipe.

Author: EliahKagan

Makefile

@@ -126,8 +126,8 @@ bench-gix-config:
 
 check-msrv-on-ci: ## Check the minimal support rust version for currently installed Rust version
 	rustc --version
-	cargo check --locked --package gix
-	cargo check --locked --package gix --no-default-features --features async-network-client,max-performance
+	cargo build --locked --package gix
+	cargo build --locked --package gix --no-default-features --features async-network-client,max-performance
 
 ##@ Maintenance
 

justfile

@@ -246,8 +246,8 @@ check-size:
 # Check the MSRV, *if* the toolchain is set and `Cargo.lock` is downgraded (used on CI)
 ci-check-msrv:
     rustc --version
-    cargo check --locked -p gix
-    cargo check --locked -p gix --no-default-features --features async-network-client,max-performance
+    cargo build --locked -p gix
+    cargo build --locked -p gix --no-default-features --features async-network-client,max-performance
 
 # Enter a nix-shell able to build on macOS
 nix-shell-macos: