Add heading attribute to glossary.md (#1829)

Add heading attributes[1] to avoid ID changes in translation.

[1]: https://rust-lang.github.io/mdBook/format/markdown.html#heading-attributes

Related: #1825

---------

Co-authored-by: Martin Geisler <[email protected]>

Author: mobyw

src/glossary.md

@@ -1,23 +1,25 @@
-# Glossary
+<!-- i18n:comment Please keep { #glossary } untranslated. -->
+
+# Glossary { #glossary }
 
 The following is a glossary which aims to give a short definition of many Rust
 terms. For translations, this also serves to connect the term back to the
 English original.
 
 <style>
-h1 ~ ul {
+h1#glossary ~ ul {
     list-style: none;
     padding-inline-start: 0;
 }
 
-h1 ~ ul > li {
+h1#glossary ~ ul > li {
     /* Simplify with "text-indent: 2em hanging" when supported:
        https://caniuse.com/mdn-css_properties_text-indent_hanging */
     padding-left: 2em;
     text-indent: -2em;
 }
 
-h1 ~ ul > li:first-line {
+h1#glossary ~ ul > li:first-line {
     font-weight: bold;
 }
 </style>