Fix codecov by adding a deeper "fetch-depth" to GitHub Actions

I'm not sure when this became a requirement, but apparently in the
past few days codecov started needing more commit history.

Author: TheBlueMatt

.github/workflows/build.yml

@@ -33,6 +33,8 @@ jobs:
     steps:
       - name: Checkout source code
         uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
       - name: Install Rust ${{ matrix.toolchain }} toolchain
         uses: actions-rs/toolchain@v1
         with: