dns/bind: bump 26.7 package revision to 7

[bryanwieg]

Summary

• bump os-bind-rp for OPNsense 26.7 from 26.7_6 to 26.7_7
• produce a fresh package and source-release identity after GitHub permanently tombstoned the malformed immutable 26.7_6 source-release tag
• leave plugin source, dependencies, conflicts, minimum OPNsense version, and immutable release provenance unchanged

Context

The 26.7_6 package channel was built, published, and publicly installation-verified successfully. Its separate source Release was published without assets before PR 99 corrected the immutable-release ordering. GitHub permanently prevents reuse of that old tag name, even after deleting the empty Release and tag.

Verification

• isolated diff: PLUGIN_REVISION 6 -> 7 only
• git diff check passed
• independent specification, release/provenance, code-simplification, test-suite, and documentation-impact reviews: no blocking findings
• canonical master-based BIND tests run in this PR workflow