Update Centipede to 7a20b4e (#10021)

Update Centipede to its latest version (Jan 14 -> Mar 28).
Will push another PR to ClusterFuzz to capture the new crash log outputs
so that the RegEx in ClusterFuzz is consistent with the format test
cases in Centipede.

infra/base-images/base-builder/Dockerfile

@@ -134,7 +134,7 @@ RUN precompile_honggfuzz
 RUN cd $SRC && \
     git clone https://github.com/google/centipede.git && \
     cd centipede && \
-    git checkout eb91dd2157710e6c82579f8be19d7fab9423b781 && \
+    git checkout 7a20b4e58c8363df0fb73bc28927241043bc0dc2 && \
     rm -rf .git
 
 COPY precompile_centipede /usr/local/bin/