Bump MSRV from 1.56.0 to 1.56.1

In this way we can continue using reqwest v0.11, whose MSRV is now
1.56.1
The only difference between v1.56.0 and v1.56.1 is a bug fix for
CVE-2021-42574.

.github/workflows/cont_integration.yml

@@ -12,7 +12,7 @@ jobs:
         rust:
           - version: 1.60.0 # STABLE
             clippy: true
-          - version: 1.56.0 # MSRV
+          - version: 1.56.1 # MSRV
         features:
           - default
           - minimal
@@ -146,7 +146,7 @@ jobs:
       - run: sudo apt-get update || exit 1
       - run: sudo apt-get install -y libclang-common-10-dev clang-10 libc6-dev-i386 || exit 1
       - name: Set default toolchain
-        run: rustup default 1.56.0 # STABLE
+        run: rustup default 1.56.1 # STABLE
       - name: Set profile
         run: rustup set profile minimal
       - name: Add target wasm32