CI: Fix pinning

Pin `cc` and fix the `syn` pin.

Author: tcharding

bitcoin/contrib/test.sh

@@ -25,10 +25,12 @@ fi
 
 # Pin dependencies as required if we are using MSRV toolchain.
 if cargo --version | grep "1\.41"; then
+    cargo update -p cc --precise 1.0.77
     # 1.0.157 uses syn 2.0 which requires edition 2018
     cargo update -p serde --precise 1.0.156
-    # 1.0.108 uses `matches!` macro so does not work with Rust 1.41.1, bad `syn` no biscuit.
-    cargo update -p syn --precise 1.0.107
+
+    # latest arrayvec build fails because of `track_caller`.
+    cargo update -p arrayvec --precise 0.7.2
 fi
 
 # Pin dependencies as above (required for no-std tests that use Rust 1.47 toolchain).