Enable msan

.github/workflows/sanitizer.yml

diff --git a/.github/workflows/sanitizer.yml b/.github/workflows/sanitizer.yml
index fbc9844..57470ba 100644
--- a/.github/workflows/sanitizer.yml
+++ b/.github/workflows/sanitizer.yml
@@ -18,8 +18,7 @@
       fail-fast: false
       matrix:
         build_type: ['Debug', 'RelWithDebInfo']
-        sanitizer: ['asan', 'ubsan', 'tsan']
-        # TODO: add 'msan' above. currently failing and needs investigation.
+        sanitizer: ['asan', 'ubsan', 'tsan', 'msan']
     steps:
     - uses: actions/checkout@v2