mimemagic not compaction-friendly

[HoneyryderChuck]

I'm getting an error which is frequently reproducible in CI and locally via docker, when GC auto-compact is turned on.

> bundle exec ruby -e 'GC.auto_compact = true if GC.respond_to?(:auto_compact=) ; require "mimemagic"'
/usr/local/bundle/ruby/3.0.0/gems/nokogiri-1.13.1-x86_64-linux/lib/nokogiri/xml/searchable.rb:264: [BUG] Segmentation fault at 0x000000000000004c
ruby 3.0.3p157 (2021-11-24 revision 3fb7d2cadc) [x86_64-linux]

-- Control frame information -----------------------------------------------
c:0011 p:0105 s:0067 e:000065 METHOD /usr/local/bundle/ruby/3.0.0/gems/nokogiri-1.13.1-x86_64-linux/lib/nokogiri/xml/searchable.rb:264
c:0010 p:0005 s:0057 e:000056 METHOD /usr/local/bundle/ruby/3.0.0/gems/nokogiri-1.13.1-x86_64-linux/lib/nokogiri/xml/searchable.rb:52
c:0009 p:0016 s:0047 e:000045 BLOCK  /usr/local/bundle/ruby/3.0.0/gems/mimemagic-0.4.3/lib/mimemagic/tables.rb:80
c:0008 p:0008 s:0038 e:000037 BLOCK  /usr/local/bundle/ruby/3.0.0/gems/nokogiri-1.13.1-x86_64-linux/lib/nokogiri/xml/node_set.rb:233 [FINISH]
c:0007 p:---- s:0034 e:000033 CFUNC  :upto
c:0006 p:0019 s:0029 e:000028 METHOD /usr/local/bundle/ruby/3.0.0/gems/nokogiri-1.13.1-x86_64-linux/lib/nokogiri/xml/node_set.rb:232
c:0005 p:0041 s:0025 e:000024 METHOD /usr/local/bundle/ruby/3.0.0/gems/mimemagic-0.4.3/lib/mimemagic/tables.rb:79
c:0004 p:0029 s:0014 e:000013 TOP    /usr/local/bundle/ruby/3.0.0/gems/mimemagic-0.4.3/lib/mimemagic.rb:8 [FINISH]
c:0003 p:---- s:0011 e:000010 CFUNC  :require
c:0002 p:0034 s:0006 e:000005 EVAL   -e:1 [FINISH]
c:0001 p:0000 s:0003 E:000cb0 (none) [FINISH]

-- Ruby level backtrace information ----------------------------------------
-e:1:in `<main>'
-e:1:in `require'
/usr/local/bundle/ruby/3.0.0/gems/mimemagic-0.4.3/lib/mimemagic.rb:8:in `<top (required)>'
/usr/local/bundle/ruby/3.0.0/gems/mimemagic-0.4.3/lib/mimemagic/tables.rb:79:in `parse_database'
/usr/local/bundle/ruby/3.0.0/gems/nokogiri-1.13.1-x86_64-linux/lib/nokogiri/xml/node_set.rb:232:in `each'
/usr/local/bundle/ruby/3.0.0/gems/nokogiri-1.13.1-x86_64-linux/lib/nokogiri/xml/node_set.rb:232:in `upto'
/usr/local/bundle/ruby/3.0.0/gems/nokogiri-1.13.1-x86_64-linux/lib/nokogiri/xml/node_set.rb:233:in `block in each'
/usr/local/bundle/ruby/3.0.0/gems/mimemagic-0.4.3/lib/mimemagic/tables.rb:80:in `block in parse_database'
/usr/local/bundle/ruby/3.0.0/gems/nokogiri-1.13.1-x86_64-linux/lib/nokogiri/xml/searchable.rb:52:in `search'
/usr/local/bundle/ruby/3.0.0/gems/nokogiri-1.13.1-x86_64-linux/lib/nokogiri/xml/searchable.rb:264:in `extract_params'

-- Machine register context ------------------------------------------------
 RIP: 0x00007fccc87b0500 RBP: 0x0000000000000034 RSP: 0x00007fff3b7acf00
 RAX: 0x0000000000000000 RBX: 0x00005626cf776df0 RCX: 0x000170c100100001
 RDX: 0x0000000000000000 RDI: 0x000170c100100001 RSI: 0x0000000000000034
  R8: 0x0000000000000000  R9: 0x0000000000000001 R10: 0x0000000000000002
...

Although it points to nokogiri, it's not reproducible if I require it as above.

cc @tenderlove