IPatchSeriesMetadata: the PR URL is not actually optional

It _used_ to be optional when there was also a way to run GitGitGadget
in a local repository on a branch that had an upstream branch
configured, in which case there was no PR to work with.

But after I dropped the CLI in 6d397b0 (Remove support for the CLI
mode, 2023-12-31), GitGitGadget really only works with PRs.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

lib/patch-series-metadata.ts

@@ -1,5 +1,5 @@
 export interface IPatchSeriesMetadata {
-    readonly pullRequestURL?: string;
+    readonly pullRequestURL: string;
     baseCommit: string;
     baseLabel: string;
     headCommit: string;

tests/patch-series.test.ts

@@ -87,6 +87,7 @@ class PatchSeriesTest extends PatchSeries {
         const thisAuthor = "GitGitGadget <gitgitgadget@gmail.com>";
         const senderName = "Nguyễn Thái Ngọc Duy";
         const prMeta = {
+            pullRequestURL: "",
             baseCommit: "",
             baseLabel: "",
             headCommit: "",

tests/project-options.test.ts

@@ -36,6 +36,7 @@ test("project options", async () => {
     await class X extends PatchSeries {
         public static async test(): Promise<void> {
             const prMeta = {
+                pullRequestURL: "",
                 baseCommit: options2.baseCommit,
                 baseLabel: "upstream/main",
                 headCommit: options2.headCommit,