chore(CI): Relax MSRV to 1.56.1

- Previously raised to `1.59.0` for CI to pass.
- With an MSRV lock file committed this is no longer necessary.

Signed-off-by: Brennan Kinney <5098581+polarathene@users.noreply.github.com>

.github/workflows/msrv.yml

@@ -9,7 +9,7 @@ jobs:
     strategy:
       matrix:
         rust:
-          - 1.59.0
+          - 1.56.1
           - stable
           - beta
           - nightly
@@ -48,7 +48,7 @@ jobs:
     strategy:
       matrix:
         rust:
-          - 1.59.0
+          - 1.56.1
           - stable
           - beta
           - nightly
@@ -67,14 +67,14 @@ jobs:
         run: cp Cargo.lock.msrv Cargo.lock
 
       - name: Run cargo test
-        if: matrix.rust != 'nightly' && matrix.rust != '1.59.0'
+        if: matrix.rust != 'nightly' && matrix.rust != '1.56.1'
         uses: actions-rs/cargo@v1
         with:
           command: test
           args: --all-features
 
       - name: Run cargo test (nightly)
-        if: matrix.rust == '1.59.0'
+        if: matrix.rust == '1.56.1'
         continue-on-error: true
         uses: actions-rs/cargo@v1
         with:
@@ -127,7 +127,7 @@ jobs:
       - name: Install toolchain
         uses: actions-rs/toolchain@v1
         with:
-          toolchain: 1.59.0
+          toolchain: 1.56.1
           override: true
           components: clippy
 
@@ -147,7 +147,7 @@ jobs:
     strategy:
       matrix:
         rust:
-          - 1.59.0
+          - 1.56.1
           - stable
 
     steps: