fix: Improve compatibility with PHP 8.5

[matsuo]

This PR addresses the following two issues to improve compatibility with PHP 8.5 and ensure that CI jobs pass on PHP 8.5.

• PHP 8.5 Deprecation: SplObjectStorage::contains() deprecated in RemoveSpansWithoutAttributes.php #476
• PHP 8.5 Deprecation: "Using null as an array offset is deprecated, use an empty string instead" in URISchemeRegistry.php #483

The following deprecated messages were displayed when running tests/index.php in the htmlpurifier repository using PHP 8.5.

% /opt/homebrew/opt/php@8.5/bin/php tests/index.php
All HTML Purifier tests on PHP 8.5.2
Exception 1!
Unexpected PHP Error [Using null as an array offset is deprecated, use an empty string instead] severity [8192] in [/tmp/htmlpurifier/library/HTMLPurifier/URISchemeRegistry.php line 55]
	in testDefaultSchemeNull
	in HTMLPurifier_AttrDef_URITest
Exception 2!
Unexpected PHP Error [Using null as an array offset is deprecated, use an empty string instead] severity [8192] in [/tmp/htmlpurifier/library/HTMLPurifier/URISchemeRegistry.php line 58]
	in testDefaultSchemeNull
	in HTMLPurifier_AttrDef_URITest
Exception 3!
Unexpected PHP Error [Method SplObjectStorage::attach() is deprecated since 8.5, use method SplObjectStorage::offsetSet() instead] severity [8192] in [/tmp/htmlpurifier/library/HTMLPurifier/Injector/RemoveSpansWithoutAttributes.php line 77]
	in testSingleSpan
	in HTMLPurifier_Injector_RemoveSpansWithoutAttributesTest
Exception 4!
Unexpected PHP Error [Method SplObjectStorage::contains() is deprecated since 8.5, use method SplObjectStorage::offsetExists() instead] severity [8192] in [/tmp/htmlpurifier/library/HTMLPurifier/Injector/RemoveSpansWithoutAttributes.php line 88]
	in testSingleSpanWithAttributes
	in HTMLPurifier_Injector_RemoveSpansWithoutAttributesTest

(snip)

Exception 23!
Unexpected PHP Error [Method SplObjectStorage::detach() is deprecated since 8.5, use method SplObjectStorage::offsetUnset() instead] severity [8192] in [/tmp/htmlpurifier/library/HTMLPurifier/Injector/RemoveSpansWithoutAttributes.php line 89]
	in testDeeplyNestedSpan
	in HTMLPurifier_Injector_RemoveSpansWithoutAttributesTest

(snip)

Thank you.

[Copilot]

Pull request overview

This pull request aims to eliminate PHP 8.5 deprecation notices observed when running the test suite, improving forward compatibility of HTMLPurifier’s URI handling and an injector’s internal bookkeeping.

Changes:

• Updates RemoveSpansWithoutAttributes to use SplObjectStorage::offsetSet/offsetExists/offsetUnset instead of deprecated attach/contains/detach.
• Adds an early-return in URISchemeRegistry::getScheme() intended to avoid “null as an array offset” deprecations on PHP 8.5.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
library/HTMLPurifier/URISchemeRegistry.php	Adds a guard intended to prevent PHP 8.5 null-array-offset deprecations during scheme lookup.
library/HTMLPurifier/Injector/RemoveSpansWithoutAttributes.php	Replaces deprecated SplObjectStorage methods with the recommended offset* equivalents.

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