Fix -p servo lib target build (and fix CI check accordingly) (#43170)

the `-p servo` (formerly libservo) lib target was busted for anyone
genuinely consuming it as a library, but we didn’t catch it because the
CI job designed to check it built `-p servo` with --all-targets, which
unlike library consumers pulls in [dev-dependencies].

this patch fixes the compile error, and fixes the CI check to build `-p
servo` in a more realistic configuration.

Testing: tested in CI, and locally with `cargo build -p servo --locked`
Fixes: #43168

Signed-off-by: delan azabani <dazabani@igalia.com>

.github/workflows/linux.yml

@@ -288,7 +288,7 @@ jobs:
           # We can remove this after upgrading to Rust 1.90, where lld will be the default.
           RUSTFLAGS: "-C link-arg=-fuse-ld=lld"
         run: |
-          cargo +${{ steps.msrv.outputs.rust_version }} build -p servo --locked --all-targets
+          cargo +${{ steps.msrv.outputs.rust_version }} build -p servo --locked
 
   # Runs the underlying job (“workload”) on a self-hosted runner if available.
   runner-select-coverage:

.github/workflows/mac-arm64.yml

@@ -249,4 +249,4 @@ jobs:
           toolchain: ${{ steps.msrv.outputs.rust_version }}
       - name: Compile libservo with MSRV
         run: |
-          cargo +${{ steps.msrv.outputs.rust_version }} build -p servo --locked --all-targets
+          cargo +${{ steps.msrv.outputs.rust_version }} build -p servo --locked

.github/workflows/mac.yml

@@ -257,4 +257,4 @@ jobs:
           toolchain: ${{ steps.msrv.outputs.rust_version }}
       - name: Compile libservo with MSRV
         run: |
-          cargo +${{ steps.msrv.outputs.rust_version }} build -p servo --locked --all-targets
+          cargo +${{ steps.msrv.outputs.rust_version }} build -p servo --locked

.github/workflows/windows.yml

@@ -266,4 +266,4 @@ jobs:
           toolchain: ${{ steps.msrv.outputs.rust_version }}
       - name: Compile libservo with MSRV
         run: |
-          cargo +${{ steps.msrv.outputs.rust_version }} build -p servo --locked --all-targets
+          cargo +${{ steps.msrv.outputs.rust_version }} build -p servo --locked