[GITEA] Only pass selected repository IDs to pagination

- Backport of https://codeberg.org/forgejo/forgejo/pulls/1848
- `ReposParam` is passed to the pagination as value for the `repos`
query. It should paginate to other pages with only the selected
repositories, which was currently not the case, but was already the case
for the links in the selectable items.
- Fix the wrong value being passed for issues/pulls lists.
- Fix the formatting of repository query value for milestones lists.
- Added integration testing.
- Resolves https://codeberg.org/forgejo/forgejo/issues/1836

(cherry picked from commit c648e5ab3a)

routers/web/user/home.go

@@ -315,9 +315,18 @@ func Milestones(ctx *context.Context) {
 	ctx.Data["RepoIDs"] = repoIDs
 	ctx.Data["IsShowClosed"] = isShowClosed
 
+	// Convert []int64 to string
+	reposParam, err := json.Marshal(repoIDs)
+	if err != nil {
+		ctx.ServerError("json.Marshal", err)
+		return
+	}
+
+	ctx.Data["ReposParam"] = string(reposParam)
+
 	pager := context.NewPagination(pagerCount, setting.UI.IssuePagingNum, page, 5)
 	pager.AddParam(ctx, "q", "Keyword")
-	pager.AddParam(ctx, "repos", "RepoIDs")
+	pager.AddParam(ctx, "repos", "ReposParam")
 	pager.AddParam(ctx, "sort", "SortType")
 	pager.AddParam(ctx, "state", "State")
 	ctx.Data["Page"] = pager
@@ -690,7 +699,11 @@ func buildIssueOverview(ctx *context.Context, unitType unit.Type) {
 	}
 
 	// Convert []int64 to string
-	reposParam, _ := json.Marshal(opts.RepoIDs)
+	reposParam, err := json.Marshal(selectedRepoIDs)
+	if err != nil {
+		ctx.ServerError("json.Marshal", err)
+		return
+	}
 
 	ctx.Data["ReposParam"] = string(reposParam)