build!: enable md4 for testing.

Operators Note: In newer versions of ubuntu the MD4 hashing algorithm
is disabled by default.  To enable it the openssl config needs to be
updated in a manner similar to what's being done here.  Alternatively,
you can set the `FEATURES['ENABLE_BLAKE2B_HASHING']` setting to `True`
which will switch to a newer hashing algorithm where MD4 was previously
used.

Because this hashing is being used as a part of the edx-platform caching
mechanism, this will effectively clear the cache for the items that use
this hash. The will impact any items where the cache key might have been
too big to store in memcache so it's hard to predict exactly which items
will be impacted.

BREAKING CHANGE: See the operator note above for more details as this
may break for users transitioning from Ubuntu 20.04 to newer versions.

.github/workflows/unit-tests.yml

@@ -66,7 +66,26 @@ jobs:
 
       - name: install system requirements
         run: |
-          sudo apt-get update && sudo apt-get install libmysqlclient-dev libxmlsec1-dev lynx
+          sudo apt-get update && sudo apt-get install libmysqlclient-dev libxmlsec1-dev lynx openssl
+
+      # This is needed until the ENABLE_BLAKE2B_HASHING can be removed and we
+      # can stop using MD4 by default.
+      - name: enable md4 hashing in libssl
+        run: |
+          cat <<EOF | sudo tee /etc/ssl/openssl.cnf
+          [openssl_init]
+          providers = provider_sect
+
+          [provider_sect]
+          default = default_sect
+          legacy = legacy_sect
+
+          [default_sect]
+          activate = 1
+
+          [legacy_sect]
+          activate = 1
+          EOF
 
       - name: install mongo version
         run: |