Add Mono download to Ubuntu test env #3277

Job	Run time
Pretest	1m 1s
Pretest	1m 1s
GitHub Integration Tests	5m 1s
GitHub Integration Tests	5m 1s
Bitbucket Server Integration Tests	6m 51s
Bitbucket Server Integration Tests	6m 51s
Azure Integration Tests (ubuntu)	4m 33s
Azure Integration Tests (ubuntu)	4m 33s
GitLab Integration Tests (ubuntu)	7m 24s
GitLab Integration Tests (ubuntu)	7m 27s
Azure Integration Tests (windows)	6m 45s
Azure Integration Tests (windows)	6m 45s
Unit Tests (ubuntu)	2m 59s
Unit Tests (ubuntu)	2m 59s
GitLab Integration Tests (windows)	9m 15s
GitLab Integration Tests (windows)	9m 15s
Azure Integration Tests (macos)	6m 4s
Azure Integration Tests (macos)	6m 4s
Unit Tests (windows)	10m 16s
Unit Tests (windows)	10m 16s
GitLab Integration Tests (macos)	9m 12s
GitLab Integration Tests (macos)	9m 12s
Unit Tests (macos)	3m 0s
Unit Tests (macos)	3m 0s
Scan Repository Tests (ubuntu)	12m 45s
Scan Repository Tests (ubuntu)	12m 45s
Scan Repository Tests (windows)	26m 24s
Scan Repository Tests (windows)	26m 24s
Scan Repository Tests (macos)	18m 46s
Scan Repository Tests (macos)	18m 46s
Scan Pull Request Tests (ubuntu)	16m 38s
Scan Pull Request Tests (ubuntu)	16m 38s
Scan Pull Request Tests (windows)	29m 1s
Scan Pull Request Tests (windows)	29m 1s
Scan Pull Request Tests (macos)	20m 41s
Scan Pull Request Tests (macos)	20m 41s
Package Handlers Tests (ubuntu)	3m 39s
Package Handlers Tests (ubuntu)	3m 39s
Package Handlers Tests (windows)	13m 11s
Package Handlers Tests (windows)	13m 11s
Package Handlers Tests (macos)	4m 6s
Package Handlers Tests (macos)	4m 6s
	7h 15m 7s

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