Pin boring version to 4.13 for MSRV tests.

Boring 4.14 requires Rust 1.80

.github/workflows/build.yml

@@ -7,7 +7,7 @@ jobs:
     strategy:
       matrix:
         # nightly, MSRV, and latest stable
-        toolchain: [nightly, 1.72, 1.82.0]
+        toolchain: [nightly, 1.72.0, 1.82.0]
     runs-on: ubuntu-latest
     # Only run on "pull_request" event for external PRs. This is to avoid
     # duplicate builds for PRs created from internal branches.
@@ -34,6 +34,10 @@ jobs:
           toolchain: ${{ matrix.toolchain }}
           components: rustfmt, clippy
 
+      - name: Pin crates to versions for MSRV
+        run: |
+          [[ ${{ matrix.toolchain }} != 1.72.0 ]] || cargo update -p boring --precise 4.13.0
+
       - name: Run cargo fmt
         run: cargo fmt --all -- --check