devel/rubygem-opentelemetry-instrumentation-rack: update to 0.26.0

Changes: https://github.com/open-telemetry/opentelemetry-ruby/releases
Changes: https://github.com/open-telemetry/opentelemetry-ruby-contrib/blob/main/instrumentation/rack/CHANGELOG.md
PR: 284152
Approved by: maintainer (timeout)