Editorial: merge two adjacent <emu-grammar> elements

(It's the only such occurrence in the spec.)
Merging them into a single element makes it easier
to programmatically associate the following algorithm
with both productions, rather than just the second.

spec.html

@@ -29362,8 +29362,11 @@ <h1>Static Semantics: CharacterValue</h1>
 
       <emu-clause id="sec-static-semantics-sourcetext">
         <h1>Static Semantics: SourceText</h1>
-        <emu-grammar>UnicodePropertyNameCharacters :: UnicodePropertyNameCharacter UnicodePropertyNameCharacters?</emu-grammar>
-        <emu-grammar>UnicodePropertyValueCharacters :: UnicodePropertyValueCharacter UnicodePropertyValueCharacters?</emu-grammar>
+        <emu-grammar>
+          UnicodePropertyNameCharacters :: UnicodePropertyNameCharacter UnicodePropertyNameCharacters?
+
+          UnicodePropertyValueCharacters :: UnicodePropertyValueCharacter UnicodePropertyValueCharacters?
+        </emu-grammar>
         <emu-alg>
           1. Return the List, in source text order, of Unicode code points in the source text matched by this production.
         </emu-alg>