CI: msrv: remove update syn

Author: RCasatta

.github/workflows/test.yml

@@ -88,7 +88,6 @@ jobs:
           cargo update -p serde --precise 1.0.156
           cargo update -p regex --precise 1.7.3
           cargo update -p quote --precise 1.0.28
-          cargo update -p syn:2.0.37 --precise 2.0.32
           cargo update -p proc-macro2 --precise 1.0.63
         if: ${{ matrix.toolchain == '1.48.0' }}
       - run: cargo build