[extension/oidcauthextension] Remove deprecated net.Dialer.DualStack from provider config HTTP transport

[codeboten]

processProviderConfig's HTTP transport sets net.Dialer{DualStack: true}. DualStack has been deprecated since Go 1.12 - Fast Fallback (RFC 6555 Happy Eyeballs) is enabled by default and this field is now a no-op. Currently suppressed with //nolint:staticcheck.

Same situation as the signalfxexporter dimension client (see #50430) - fix should just be removing the field.

[github-actions]

Pinging code owners:

• extension/oidcauth: @asweet-confluent

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