[sonic-slave]: Fix redis version during pip3 install (#9317)

The recent release of redis 4.0.0 or newer (for python3) breaks sonic-config-engine unit test. Fix to last known good version.
ref: https://pypi.org/project/redis/#history

Author: qiluo-msft

sonic-slave-bullseye/Dockerfile.j2

@@ -444,7 +444,7 @@ RUN pip3 install "PyYAML==5.4.1"
 RUN pip3 install "lxml==4.6.2"
 
 # For sonic-platform-common testing
-RUN pip3 install redis
+RUN pip3 install redis==3.5.3
 
 # For vs image build
 RUN pip3 install pexpect==4.8.0

sonic-slave-buster/Dockerfile.j2

@@ -457,7 +457,7 @@ RUN pip2 install "lxml==4.6.2"
 RUN pip3 install "lxml==4.6.2"
 
 # For sonic-platform-common testing
-RUN pip3 install redis
+RUN pip3 install redis==3.5.3
 
 # For vs image build
 RUN pip2 install pexpect==4.6.0

sonic-slave-stretch/Dockerfile.j2

@@ -365,7 +365,7 @@ RUN pip3 install "lxml==4.6.2"
 
 
 # For sonic-platform-common testing
-RUN pip3 install redis
+RUN pip3 install redis==3.5.3
 
 # For vs image build
 RUN pip2 install pexpect==4.6.0