ci: exclude Mongo DB downloaded files from Git repository

Rationale: `git` commands such as `git status` don't list these files
anymore which makes the output much more readable.

.gitignore

@@ -140,4 +140,7 @@ terraform.tfstate*
 
 #helm chart
 deploy/asapo_helm_chart/asapo/Chart.lock
-deploy/asapo_helm_chart/asapo/charts/*.tgz
\ No newline at end of file
+deploy/asapo_helm_chart/asapo/charts/*.tgz
+
+# Files downloaded for Mongo DB
+mongo-c-driver-*