Fix project_ids query param

I initially created the project_ids query param
using a different method for handling arrays.
I should have gone the simpler path of just
using a comma separated list.

ee/app/assets/javascripts/analytics/repository_analytics/utils.js

 export const getProjectIdQueryParams = projects =>
-  projects.map(project => `project_ids[]=${project.id}`).join('&');
+  `project_ids=${projects.map(project => project.id).join(',')}`;

ee/changelogs/unreleased/215130-fix-project-id-query-params.yml

+---
+title: Fix project_ids query param for downloading coverage CSV report
+merge_request: 42497
+author:
+type: fixed

ee/spec/frontend/analytics/repository_analytics/components/group_repository_analytics_spec.js

@@ -90,7 +90,7 @@ describe('Group repository analytics app', () => {
         });
 
         it('renders primary action as a link with one project ID as a parameter', () => {
-          const expectedPath = `${groupAnalyticsCoverageReportsPathWithDates}&project_ids[]=${groupProjectsData[0].id}`;
+          const expectedPath = `${groupAnalyticsCoverageReportsPathWithDates}&project_ids=${groupProjectsData[0].id}`;
 
           expect(findCodeCoverageDownloadButton().attributes('href')).toBe(expectedPath);
         });
@@ -111,7 +111,7 @@ describe('Group repository analytics app', () => {
     });
 
     describe('when selecting a date range', () => {
-      const projectIdParams = '&project_ids[]=1&project_ids[]=2';
+      const projectIdParams = '&project_ids=1,2';
 
       it.each`
         date  | expected

ee/spec/frontend/analytics/repository_analytics/utils_spec.js

@@ -4,7 +4,7 @@ describe('group repository analytics util functions', () => {
   describe('getProjectIdQueryParams', () => {
     it('returns query param string project ids', () => {
       const projects = [{ id: 1 }, { id: 2 }];
-      const expectedString = 'project_ids[]=1&project_ids[]=2';
+      const expectedString = 'project_ids=1,2';
 
       expect(getProjectIdQueryParams(projects)).toBe(expectedString);
     });