ci: pin cc for MSRV

Author: apoelstra

.github/workflows/rust.yml

@@ -107,4 +107,4 @@ jobs:
           toolchain: ${{ matrix.rust }}
           override: true
       - name: Running cargo in release mode
-        run: cargo test --features="global-context" --release
+        run: cargo update -p cc --precise 1.0.94 && cargo test --features="global-context" --release

contrib/test.sh

@@ -8,6 +8,11 @@ rustc --version
 # Make all cargo invocations verbose
 export CARGO_TERM_VERBOSE=true
 
+# Pin dependencies as required if we are using MSRV toolchain.
+if cargo --version | grep "1\.56"; then
+    cargo update -p cc --precise 1.0.94
+fi
+
 # Defaults / sanity checks
 cargo build --all
 cargo test --all