fix(tests): change workflow to use rust 1.56.0

Author: oyvindln

.github/workflows/test.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        build: [stable, nightly, 1.50.0, macos, windows, mingw]
+        build: [stable, nightly, 1.56.0, macos, windows, mingw]
         include:
           - build: stable
             os: ubuntu-latest