fix(deps): update module go.opentelemetry.io/auto to v0.21.0

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
go.opentelemetry.io/auto	v0.20.0 -> v0.21.0

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Release Notes

open-telemetry/opentelemetry-go-instrumentation (go.opentelemetry.io/auto)

v0.21.0

Compare Source

[!WARNING]
The net/http instrumentation support for versions < 1.19 has been dropped.

[!WARNING]
The database/sql instrumentation support for versions < 1.19 has been dropped.

[!NOTE]
This is the last release version that will support building the auto-instrumentation CLI using Go 1.22.
The next release will require development to be done using Go >= 1.23.

Added

• Update instrumentation for net/http to support Go 1.24 SwissMap. (#​1636)
• Cache offsets for Go 1.22.12. (#​1743)
• Cache offsets for Go 1.23.6. (#​1743)
• Cache offsets for golang.org/x/net 0.35.0. (#​1783)
• Cache offsets for Go 1.24.0. (#​1795, #​1798)

Changed

• Unused support for instrumentation of Go < 1.19 has been dropped. (#​1815)

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