Fix GitHub refresh token detection

[danielgaskins]

What changed

• Match the documented 76-character body used by ghr_ refresh tokens
• Require a delimiter or end of input so longer values are not partially matched
• Extract only the token and exclude any trailing delimiter
• Add coverage for delimiter and EOF cases, plus incorrect lengths

Testing

• GOMAXPROCS=2 go test -p 1 ./...

Fixes #305

[greptile-apps]

Greptile Summary

Updates GitHub refresh-token detection to require a 76-character body and a trailing boundary while extracting only the token.

• Synchronizes the generated rule and bundled configuration.
• Adds delimiter, EOF, and invalid-length coverage.

Confidence Score: 5/5

The PR appears safe to merge.

The rule source, generated configuration, extraction group, and boundary tests are aligned, with no concrete blocking or non-blocking defect identified.

Important Files Changed

Filename	Overview
cmd/generate/config/rules/github.go	Updates the refresh-token regex, extraction group, and validation samples consistently.
cmd/generate/config/rules/github_test.go	Covers delimiter and EOF matches plus rejected token lengths.
config/betterleaks.toml	Keeps the bundled generated rule aligned with its Go source.

_{Reviews (1): Last reviewed commit: "Fix GitHub refresh token detection" | Re-trigger Greptile}