ci: pin libc for msrv job

Author: seanmonstar

.github/workflows/ci.yml

@@ -30,16 +30,15 @@ jobs:
       matrix:
         rust:
           - 1.13
-        target:
-          - x86_64-unknown-linux-gnu
 
     steps:
     - uses: actions/checkout@v3
     - name: Run tests
       run: |
         rustup default ${{ matrix.rust }}
-        rustup target add ${{ matrix.target }}
-        cargo test --verbose --target ${{ matrix.target }}
+        cargo update
+        cargo update -p libc --precise 0.2.26
+        cargo test --verbose
 
   test-linux:
     runs-on: ubuntu-latest