bazel: Pin Bazel to 5.x (#1279)

Github Actions bazel has been updated to the latest Bazel LTS release; 6.0

Unfortunately this breaks the libsbp build. For now we've pinned the bazel
this repository uses to version 5.4 until the version incompatibility is resolved.

.bazeliskrc

@@ -0,0 +1 @@
+USE_BAZEL_VERSION=5.4.0

.github/workflows/c.yaml

@@ -140,9 +140,15 @@ jobs:
       - uses: actions/checkout@v2
         with:
           submodules: recursive
+      - name: Install Bazel
+        run: |
+          curl -LO "https://github.com/bazelbuild/bazelisk/releases/download/v1.15.0/bazelisk-linux-amd64"
+          mkdir -p "${GITHUB_WORKSPACE}/bin/"
+          mv bazelisk-linux-amd64 "${GITHUB_WORKSPACE}/bin/bazel"
+          chmod +x "${GITHUB_WORKSPACE}/bin/bazel"
       - name: Bazel Build & Test
-        run:
-          bazel test //...
+        run: |
+          ${GITHUB_WORKSPACE}/bin/bazel test //...
 
 
   windows-2019: