Update completions.rs addressing issue #5935

[kaksv]

Added the closing brace as required.issue #5935

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This change is 

[mkaput]

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @Draggu, @kaksv, and @orizi)

a discussion (no related file):
All my comments from #5956 (review) apply here. Can you please resolve them in this PR?

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crates/cairo-lang-language-server/src/ide/completion/completions.rs line 285 at r1 (raw file):

    let completion = CompletionItem {
        label: format!("{}()", name),
        insert_text: Some(format!("{}(", name))),

This is just breaking Rust code syntax, it's not fixing the issue.