ci: Use gotestum for unit test

[doanac]

go test ./... produces so much output that human eyes struggle to find broken tests. gotestsum produces much cleaner output and summaries of failures for users.

[doanac]

@vkhoroz - just a small quality of life improvement. It changes our pages and pages of output to find a single test failure into something like:

$ gotestsum 
✓  auth (cached)
∅  cli/api
∅  cli/config
∅  cli/subcommands
∅  cli/subcommands/configs
∅  cli/subcommands/devices
∅  cli/subcommands/login
∅  cli/subcommands/updates
∅  clock
∅  cmd/cli
✓  cmd/seed (cached)
∅  context
∅  server
∅  server/ui/daemons
∅  server/ui/web/templates
∅  server/ui
✓  server/ui/web (cached)
✓  server/gateway (cached)
✓  server/ui/api (cached)
✖  cmd/server (32ms)
✓  storage (cached)
✓  storage/api (cached)
✓  storage/ostree (cached)
∅  storage/testing
∅  storage/tuf
∅  version
✓  storage/users (cached)
✓  storage/gateway (cached)

=== Skipped
=== SKIP: storage/ostree TestReadFile (0.00s)
    ostree_test.go:29: OSTree repo not available (ref not found: intel-corei7-64-lmp)

=== SKIP: storage/ostree TestReadFileNotFound (0.00s)
    ostree_test.go:45: OSTree repo not available (ref not found: intel-corei7-64-lmp)

=== Failed
=== FAIL: cmd/server TestAuthInitLocal (0.00s)
    auth_init_test.go:26: 
        	Error Trace:	/home/doanac/code/update-server/cmd/server/auth_init_test.go:26
        	Error:      	Not equal: 
        	            	expected: "loclal"
        	            	actual  : "local"
        	            	
        	            	Diff:
        	            	--- Expected
        	            	+++ Actual
        	            	@@ -1 +1 @@
        	            	-loclal
        	            	+local
        	Test:       	TestAuthInitLocal

DONE 183 tests, 2 skipped, 1 failure in 0.701s

[vkhoroz]

This is nice!

[vkhoroz]

So, there is no way to do this via go install <something>, right?

[doanac]

You can download and build with go install gotest.tools/gotestsum@latest. I figured grabbing a binary would be slightly faster