chore(mobile-ios): update dependency slather to v2.8.1 (#17385)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

mobile/mobile-ios/Gemfile

@@ -4,4 +4,4 @@ source 'https://rubygems.org'
 
 ruby '3.3.3'
 
-gem 'slather', '2.7.5'
+gem 'slather', '2.8.1'

mobile/mobile-ios/Gemfile.lock

@@ -1,9 +1,11 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    CFPropertyList (3.0.6)
+    CFPropertyList (3.0.7)
+      base64
+      nkf
       rexml
-    activesupport (7.1.3)
+    activesupport (7.1.3.4)
       base64
       bigdecimal
       concurrent-ruby (~> 1.0, >= 1.0.2)
@@ -15,34 +17,35 @@ GEM
       tzinfo (~> 2.0)
     atomos (0.1.3)
     base64 (0.2.0)
-    bigdecimal (3.1.6)
+    bigdecimal (3.1.8)
     claide (1.1.0)
     clamp (1.3.2)
     colored2 (3.1.2)
-    concurrent-ruby (1.2.3)
+    concurrent-ruby (1.3.3)
     connection_pool (2.4.1)
-    drb (2.2.0)
-      ruby2_keywords
-    i18n (1.14.1)
+    drb (2.2.1)
+    i18n (1.14.5)
       concurrent-ruby (~> 1.0)
-    minitest (5.22.2)
+    minitest (5.23.1)
     mutex_m (0.2.0)
     nanaimo (0.3.0)
-    nokogiri (1.16.2-arm64-darwin)
+    nkf (0.2.0)
+    nokogiri (1.16.6-arm64-darwin)
       racc (~> 1.4)
-    nokogiri (1.16.2-x86_64-darwin)
+    nokogiri (1.16.6-x86_64-darwin)
       racc (~> 1.4)
-    nokogiri (1.16.2-x86_64-linux)
+    nokogiri (1.16.6-x86_64-linux)
       racc (~> 1.4)
-    racc (1.7.3)
-    rexml (3.2.6)
-    ruby2_keywords (0.0.5)
-    slather (2.7.5)
+    racc (1.8.0)
+    rexml (3.2.9)
+      strscan
+    slather (2.8.1)
       CFPropertyList (>= 2.2, < 4)
       activesupport
       clamp (~> 1.3)
       nokogiri (>= 1.14.3)
       xcodeproj (~> 1.21)
+    strscan (1.0.3)
     tzinfo (2.0.6)
       concurrent-ruby (~> 1.0)
     xcodeproj (1.24.0)
@@ -59,7 +62,7 @@ PLATFORMS
   x86_64-linux
 
 DEPENDENCIES
-  slather (= 2.7.5)
+  slather (= 2.8.1)
 
 RUBY VERSION
    ruby 3.3.3p89