fix(service): Fixed shell injection vulnerability in the internal API

[lslezak]

Problem

• https://github.com/agama-project/agama/security/code-scanning/2

Solution

• Escape the path parameter so the special shell characters do not cause problems

Details

• The problem is only in the internal implementation, the DBus service just uses the default (does not allow to pass the parameter)
• But it potentially could be a problem in the future when we change the API so let's fix it, the fix is trivial anyway

[coveralls]

Pull Request Test Coverage Report for Build 11330201026

Details

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• 13 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.002%) to 70.964%

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Files with Coverage Reduction	New Missed Lines	%
service/service/lib/agama/manager.rb	13	82.76%

Totals
Change from base Build 11329642568:	0.002%
Covered Lines:	16094
Relevant Lines:	22679

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💛 - Coveralls