CI/verify-titles: verify that page tiles match what SUMMARY says

The web version renders using the SUMMARY title and ignores the file
title.

The PDF and ePUB versions use the file titles.

They ought to be the same.

.github/scripts/verify-titles.pl

@@ -0,0 +1,37 @@
+#!/usr/bin/perl
+
+my $sum = shift @ARGV;
+
+# Figure out all files in right order
+open(F, "<$sum");
+while(<F>) {
+    if($_  =~ /\[(.*)\]\(([^\)]*)\)/) {
+        my ($title, $file) = ($1, $2);
+        push @files, $file;
+        $title{$file} = $title;
+    }
+}
+close(F);
+
+sub check {
+    my ($f) = @_;
+    open(F, "<$f");
+    while(<F>) {
+        if(/^# (.*)/) {
+            # verify
+            if($1 ne $title{$f}) {
+                printf STDERR "$f says '%s', not '%s' like SUMMARY.md\n",
+                    $1, $title{$f};
+                $errors++;
+            }
+            last;
+        }
+    }
+    close(F);
+};
+
+for my $f (@files) {
+    check($f);
+}
+
+exit $errors;

.github/workflows/verify-titles.yml

@@ -0,0 +1,24 @@
+# Copyright (C) Daniel Stenberg, <[email protected]>, et al.
+
+name: verify-titles
+on:
+  push:
+    branches:
+      - master
+    paths:
+      - '**.md'
+  pull_request:
+    branches:
+      - master
+
+permissions: {}
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: build pdf
+        run: .github/scripts/verify-titles.pl SUMMARY.md
+