Readd ACM style to csl

[Siedlerchr]

JabRef searches this style when opening the preferences

Follow up fix for #7306

• Change in CHANGELOG.md described (if applicable)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• Checked documentation: Is the information available and up to date? If not created an issue at https://github.com/JabRef/user-documentation/issues or, even better, submitted a pull request to the documentation repository.

[calixtus]

Why the acm style in particular? Could this maybe a config issue?

[koppor]

Damn, did not see the PR while working on a fix at 8c49600.

[Siedlerchr]

    URL url = CitationStyle.class.getResource(STYLES_ROOT + "/acm-siggraph.csl");

[koppor]

Digging deeper:

@Siedlerchr spottet that at #7306 (comment) that

jabref/src/main/java/org/jabref/logic/citationstyle/CitationStyle.java

Line 137 in 8c49600

URL url = CitationStyle.class.getResource(STYLES_ROOT + "/acm-siggraph.csl");

It was a decision at #6010 to hard-code one specific .csl file to check whether CSL loading actually works. See especially the file-diff.