CI: Avoid testing against MSRV with test-dev-graph feature flag

We only need it for generating images of halo2_gadgets chips, and its
transitive dependencies have bumped MSRV in point releases.

.github/workflows/ci.yml

@@ -20,7 +20,7 @@ jobs:
         uses: actions-rs/cargo@v1
         with:
           command: test
-          args: --verbose --release --all --all-features
+          args: --verbose --release --workspace --features batch,dev-graph,gadget-traces,test-dependencies,unstable
 
   build:
     name: Build target ${{ matrix.target }}
@@ -51,11 +51,13 @@ jobs:
 
     steps:
       - uses: actions/checkout@v3
+      # Check bitrot with stable (as we don't need benchmarks or the test-dev-graph
+      # feature flag to work with MSRV).
       - uses: actions-rs/toolchain@v1
         with:
-          toolchain: 1.56.1
+          toolchain: stable
           override: true
-      # Build benchmarks to prevent bitrot
+      # Build benchmarks and all-features to prevent bitrot
       - name: Build benchmarks
         uses: actions-rs/cargo@v1
         with:
@@ -102,7 +104,7 @@ jobs:
         uses: actions-rs/cargo@v1
         with:
           command: tarpaulin
-          args: --all-features --timeout 600 --out Xml
+          args: --features batch,dev-graph,gadget-traces,test-dependencies,unstable --timeout 600 --out Xml
       - name: Upload coverage to Codecov
         uses: codecov/codecov-action@v3.1.1