Bump go.opentelemetry.io/build-tools/multimod in /internal/tools

Bumps [go.opentelemetry.io/build-tools/multimod](https://github.com/open-telemetry/opentelemetry-go-build-tools) from 0.6.0 to 0.8.0.
- [Release notes](https://github.com/open-telemetry/opentelemetry-go-build-tools/releases)
- [Changelog](https://github.com/open-telemetry/opentelemetry-go-build-tools/blob/main/CHANGELOG.md)
- [Commits](open-telemetry/opentelemetry-go-build-tools@v0.6.0...v0.8.0)

---
updated-dependencies:
- dependency-name: go.opentelemetry.io/build-tools/multimod
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

internal/tools/go.mod

@@ -4,5 +4,5 @@ go 1.16
 
 require (
 	go.opentelemetry.io/build-tools/dbotconf v0.8.0
-	go.opentelemetry.io/build-tools/multimod v0.6.0
+	go.opentelemetry.io/build-tools/multimod v0.8.0
 )