replace deprecated FILTER_SANITIZE_STRING (#126)

[stklcode]

resolves #126

In the following method check_theme_file() URL sanitization is applied, so we can either use FILTER_SANITIZE_URL here as well or simply pass UNSAFE_RAW in this case.

https://github.com/pluginkollektiv/antivirus/blob/e55943cdc923ab2e63297cb8d5a9132dc4ac18a6/inc/class-antivirus-checkinternals.php#L83-L87

[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (7fd71df) 36.30% compared to head (5a7e857) 36.30%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #127 +/- ## ========================================== Coverage 36.30% 36.30% Complexity 147 147 ========================================== Files 5 5 Lines 774 774 ========================================== Hits 281 281 Misses 493 493 ``` | [Files](https://app.codecov.io/gh/pluginkollektiv/antivirus/pull/127?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None) | Coverage Δ | | |---|---|---| | [inc/class-antivirus.php](https://app.codecov.io/gh/pluginkollektiv/antivirus/pull/127?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-aW5jL2NsYXNzLWFudGl2aXJ1cy5waHA=) | `17.74% <0.00%> (ø)` | |

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