os, cmd/gofmt: tests fail on ext4 with 128byte inodes due to insufficient time precision [1.25 backport]

[gopherbot]

@Jorropo requested issue #75042 to be considered for backport to the next 1.25 minor release.

@gopherbot please open backport issue for 1.25
this test has a dependency on the os.TempDir's file system time precision being equal to the clock's (time.Now) precision
This broke illumos and linux when using an older filesystem (EXT3, EXT4 with 128 bytes inodes, ...)

[Jorropo]

To be clear, on linux you need to not use tmpfs for your test tmp dir which I have no idea how common this is.
If you use ext3 for / and tmpfs for /tmp the test will pass.