chore: restore prefix-matching coverage in GetProject test

Use an 8-char slug prefix so the test exercises prefix lookup while staying
unique within the fresh test account.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: alnr

cmd/cloudx/client/command_helper_test.go

@@ -372,7 +372,7 @@ func TestCommandHelper(t *testing.T) {
 				assert.Equal(t, tc.project.Id, actual.Id)
 				assertValidProject(t, tc.project)
 
-				actual, err = authenticated.GetProject(ctx, tc.project.Slug[:len(tc.project.Slug)-1], tc.project.WorkspaceId.Get())
+				actual, err = authenticated.GetProject(ctx, tc.project.Slug[:8], tc.project.WorkspaceId.Get())
 				require.NoError(t, err)
 				assert.Equal(t, tc.project.Id, actual.Id)
 			})