pin version of gcr.io/oss-fuzz-base/base-builder

templates/tools/dockerfile/test/bazel/Dockerfile.template

@@ -14,7 +14,13 @@
   # See the License for the specific language governing permissions and
   # limitations under the License.
   
-  FROM gcr.io/oss-fuzz-base/base-builder
+  # Pinned version of the base image is used to avoid regressions caused
+  # by rebuilding of this docker image. To see available versions, you can run
+  # "gcloud container images list-tags gcr.io/oss-fuzz-base/base-builder"
+  # TODO(jtattermusch): with the latest version we'd get clang12+
+  # which makes our build fail due to new warnings being treated
+  # as errors.
+  FROM gcr.io/oss-fuzz-base/base-builder@sha256:de220fd2433cd53bd06b215770dcd14a5e74632e0215acea7401fee8cafb18da
   
   # -------------------------- WARNING --------------------------------------
   # If you are making changes to this file, consider changing

tools/dockerfile/test/bazel/Dockerfile

@@ -12,7 +12,13 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-FROM gcr.io/oss-fuzz-base/base-builder
+# Pinned version of the base image is used to avoid regressions caused
+# by rebuilding of this docker image. To see available versions, you can run
+# "gcloud container images list-tags gcr.io/oss-fuzz-base/base-builder"
+# TODO(jtattermusch): with the latest version we'd get clang12+
+# which makes our build fail due to new warnings being treated
+# as errors.
+FROM gcr.io/oss-fuzz-base/base-builder@sha256:de220fd2433cd53bd06b215770dcd14a5e74632e0215acea7401fee8cafb18da
 
 # -------------------------- WARNING --------------------------------------
 # If you are making changes to this file, consider changing