Bump idna from 3.7 to 3.15 in /docs (#725)

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docs/requirements.txt

@@ -5,7 +5,7 @@ beautifulsoup4==4.12.3
 certifi==2024.7.4
 charset-normalizer==3.3.2
 docutils==0.21.2
-idna==3.7
+idna==3.15
 imagesize==1.4.1
 Jinja2==3.1.6
 MarkupSafe==2.1.5