bump MSRV to 1.56.1

Author: apoelstra

.github/workflows/rust.yml

@@ -32,12 +32,12 @@ jobs:
     strategy:
       matrix:
         rust:
-          - 1.48.0
+          - 1.56.1
           - beta
           - stable
         os: [ ubuntu-latest, macos-latest ]
         exclude:
-          - rust: 1.48.0
+          - rust: 1.56.1
             os: macos-latest
     runs-on: ${{ matrix.os }}
     steps:
@@ -89,12 +89,12 @@ jobs:
     strategy:
       matrix:
         rust:
-          - 1.48.0
+          - 1.56.1
           - beta
           - stable
         os: [ ubuntu-latest, macos-latest ]
         exclude:
-          - rust: 1.48.0
+          - rust: 1.56.1
             os: macos-latest
     runs-on: ${{ matrix.os }}
     steps:

secp256k1-zkp-sys/README.md

@@ -33,4 +33,4 @@ against those existing symbols is left as an exercise to the reader.
 
 ## Minimum Supported Rust Version
 
-This library should always compile with any combination of features on **Rust 1.48.0**.
+This library should always compile with any combination of features on **Rust 1.56.1**.