[dev.regabi] os: disable TestDirFS until #42637 is fixed
[dev.regabi] os: disable TestDirFS until #42637 is fixed

This test is causing nearly every trybot run on dev.regabi and
dev.typeparams to fail. It's already a release blocker for Go 1.16, so
the failures on the development branches is entirely noise; and
because it causes the trybots to short-circuit, it risks masking
actual Windows-specific failures.

This CL disables the test until a proper solution is decided upon and
implemented for Go 1.16.

Updates #42637.

Change-Id: Ibc85edaed591f1c125cf0b210867aa89d2b0a4b6
Reviewed-on: https://go-review.googlesource.com/c/go/+/286213
Run-TryBot: Matthew Dempsky <e56ac2c500064424afac424d4b5e53bd0570a731@google.com>
Trust: Matthew Dempsky <e56ac2c500064424afac424d4b5e53bd0570a731@google.com>
Trust: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Than McIntosh <4b2922593166fc595a9b1a408f34f5d3817fe9d2@google.com>
Reviewed-by: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>

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