Fixes for LegacyTagsManager and SkeletonGenerator

[prisis]

fixes don't filter packages that have empty intersection with legacy tags
fixes lock writing in skeleton installer

Q	A
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	no
Related tickets	-
License	MIT
Doc PR	-

[codecov]

Codecov Report

Merging #61 into master will increase coverage by 0.84%.
The diff coverage is 86.09%.

@@             Coverage Diff             @@
##             master     #61      +/-   ##
===========================================
+ Coverage     55.26%   56.1%   +0.84%     
- Complexity      620     631      +11     
===========================================
  Files            39      39              
  Lines          1634    1663      +29     
===========================================
+ Hits            903     933      +30     
+ Misses          731     730       -1

Impacted Files	Coverage Δ	Complexity Δ
src/Automatic/Prefetcher/Prefetcher.php	0% <ø> (ø)	38 <0> (ø)	⬇️
src/Automatic/AbstractConfigurator.php	100% <100%> (ø)	13 <1> (ø)	⬇️
...tomatic/Prefetcher/TruncatedComposerRepository.php	72.72% <100%> (ø)	4 <1> (ø)	⬇️
src/Automatic/Installer/AbstractInstaller.php	100% <100%> (ø)	14 <1> (ø)	⬇️
src/Automatic/ClassFinder.php	98.23% <100%> (ø)	45 <6> (ø)	⬇️
src/Common/Package.php	100% <100%> (ø)	45 <25> (ø)	⬇️
src/Automatic/QuestionFactory.php	100% <100%> (ø)	7 <0> (ø)	⬇️
src/Automatic/ScriptExecutor.php	100% <100%> (ø)	12 <1> (ø)	⬇️
src/Automatic/LegacyTagsManager.php	100% <100%> (ø)	25 <0> (+10)	⬆️
src/Common/Installer/Installer.php	100% <100%> (ø)	8 <0> (ø)	⬇️
... and 4 more

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