Fix bikeshed warning (#1753)

Let me fix the following warnings by adding "-algorithm" to the ids.
WARNING: Multiple elements have the same id 'check-router-registration-limit':
  <h3> on line 3482, <dfn> on line 3482
Deduping, but this ID may not be stable across revisions.
WARNING: Multiple elements have the same id 'count-router-inner-conditions':
  <h3> on line 3501, <dfn> on line 3501
Deduping, but this ID may not be stable across revisions.

Author: yoshisatoyanagisawa

docs/index.bs

@@ -3479,7 +3479,7 @@ spec: storage; urlPrefix: https://storage.spec.whatwg.org/
   </section>
 
   <section algorithm>
-    <h3 id="check-router-registration-limit"><dfn>Check Router Registration Limit</dfn></h3>
+    <h3 id="check-router-registration-limit-algorithm"><dfn>Check Router Registration Limit</dfn></h3>
 
       : Input
       :: |routerRules|, a [=list of router rules=]
@@ -3495,10 +3495,10 @@ spec: storage; urlPrefix: https://storage.spec.whatwg.org/
           1. Set |result| to be the result of running [=Count Router Inner Conditions=] with |rule|["{{RouterRule/condition}}"], |result|, and 10.
           1. If |result|'s [=count router condition result/quota exceeded=] is true, return false.
       1. Return true.
-  </section> 
+  </section>
 
   <section algorithm>
-    <h3 id="count-router-inner-conditions"><dfn>Count Router Inner Conditions</dfn></h3>
+    <h3 id="count-router-inner-conditions-algorithm"><dfn>Count Router Inner Conditions</dfn></h3>
 
       : Input
       :: |condition|, a {{RouterCondition}}