Be compatible with python-werkzeug 1.0.0.

Taken from upstream:
https://github.com/beetbox/beets/commit/d43d54e21cde97f57f19486925ab56b419254cc8

diff --git a/beetsplug/web/__init__.py b/beetsplug/web/__init__.py
index f53fb3a954..21ff5d94ed 100644
--- a/beetsplug/web/__init__.py
+++ b/beetsplug/web/__init__.py
@@ -169,7 +169,7 @@ def to_python(self, value):
         return ids
 
     def to_url(self, value):
-        return ','.join(value)
+        return ','.join(str(v) for v in value)
 
 
 class QueryConverter(PathConverter):
ref='/guix/'>guix</a></td><td class='form'><form method='get'>
<input type='hidden' name='id' value='7841a624f0c94efbfeb48a5209dbd92575eacc09'/><select name='h' onchange='this.form.submit();'>
<option value='koszko' selected='selected'>koszko</option>
<option value='koszko-scripts'>koszko-scripts</option>
</select> <input type='submit' value='switch'/></form></td></tr>
<tr><td class='sub'>Wojtek's customized Guix</td><td class='sub right'></td></tr></table>
<table class='tabs'><tr><td>
<a href='/guix/about/'>about</a><a href='/guix/'>summary</a><a href='/guix/refs/?id=7841a624f0c94efbfeb48a5209dbd92575eacc09'>refs</a><a class='active' href='/guix/log/gnu/system/locale.scm'>log</a><a href='/guix/tree/gnu/system/locale.scm?id=7841a624f0c94efbfeb48a5209dbd92575eacc09'>tree</a><a href='/guix/commit/gnu/system/locale.scm?id=7841a624f0c94efbfeb48a5209dbd92575eacc09'>commit</a><a href='/guix/diff/gnu/system/locale.scm?id=7841a624f0c94efbfeb48a5209dbd92575eacc09'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/system/locale.scm'>
<input type='hidden' name='id' value='7841a624f0c94efbfeb48a5209dbd92575eacc09'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=7841a624f0c94efbfeb48a5209dbd92575eacc09'>root</a>/<a href='/guix/log/gnu?id=7841a624f0c94efbfeb48a5209dbd92575eacc09'>gnu</a>/<a href='/guix/log/gnu/system?id=7841a624f0c94efbfeb48a5209dbd92575eacc09'>system</a>/<a href='/guix/log/gnu/system/locale.scm?id=7841a624f0c94efbfeb48a5209dbd92575eacc09'>locale.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/system/locale.scm?id=7841a624f0c94efbfeb48a5209dbd92575eacc09&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2023-09-16 15:35:25 +0200'>2023-09-16</span></td><td><a href='/guix/commit/gnu/system/locale.scm?id=f2cfb4a85c82882c571274573fd7ff646d380b63'>locale: Set %default-locale-definitions to glibc/hurd on the Hurd.</a><span class='msg-avail'>...</span></td><td>Janneke Nieuwenhuizen</td></tr>
<tr><td><span title='2023-04-19 16:32:03 +0200'>2023-04-19</span></td><td><a href='/guix/commit/gnu/system/locale.scm?id=4f4c38c881d4224dc545c82253d2a8f631f95927'>locale: Add glibc 2.33 to '%default-locale-libcs'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-01-14 14:29:20 +0100'>2022-01-14</span></td><td><a href='/guix/commit/gnu/system/locale.scm?id=9d0d4b331d21cf555fdd6a8844d05389d934832c'>system: locale: Use only the current glibc.</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2021-05-15 22:55:24 +0200'>2021-05-15</span></td><td><a href='/guix/commit/gnu/system/locale.scm?id=25487c3fe6a41dd62f6e53f256392224a3be2a08'>Merge branch 'master' into core-updates</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-05-04 14:19:11 +0200'>2021-05-04</span></td><td><a href='/guix/commit/gnu/system/locale.scm?id=2e4808465d7ea5cbff0486a515cd67e3370877ce'>locale: Remove glibc 2.29 from '%default-locale-libcs'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>