internal/reflectlite: TestMirrorWithReflect failing on darwin-arm64-mn4m2zdaios builder

[bcmills]

From the darwin-arm64-mn4m2zdaios builder, a failure in the regression test for #34486 (https://build.golang.org/log/048cb165b4cd25eb76cb1c4c9b6bb2b2b93a47ce):

lldb: running program
panic: open /private/var/folders/qq/qxn86k813bn9fjxydm095rxw0000gp/T/workdir-host-darwin-amd64-zenly-ios/go/src/reflect: no such file or directory

goroutine 49 [running]:
internal/reflectlite_test.loadTypes(0x1300c6310, 0x6b, 0x102be18fe, 0x7, 0x1300c28a0)
	/private/var/folders/qq/qxn86k813bn9fjxydm095rxw0000gp/T/workdir-host-darwin-amd64-zenly-ios/go/src/internal/reflectlite/reflect_mirror_test.go:79 +0x130
internal/reflectlite_test.TestMirrorWithReflect.func1(0x1300cace0, 0x1300c6310, 0x6b, 0x102be18fe, 0x7, 0x1300c28a0)
	/private/var/folders/qq/qxn86k813bn9fjxydm095rxw0000gp/T/workdir-host-darwin-amd64-zenly-ios/go/src/internal/reflectlite/reflect_mirror_test.go:104 +0x70
created by internal/reflectlite_test.TestMirrorWithReflect
	/private/var/folders/qq/qxn86k813bn9fjxydm095rxw0000gp/T/workdir-host-darwin-amd64-zenly-ios/go/src/internal/reflectlite/reflect_mirror_test.go:102 +0x1e0
FAIL	internal/reflectlite	27.257s

The iOS builders copy the test binary and (its testdata directory, if any) over to the builder before running, so tests that require files from elsewhere in GOROOT must be skipped.

Looks like a simple fix, so I'll send a CL.

CC @cuonglm @mvdan

[gopherbot]

Change https://golang.org/cl/200657 mentions this issue: internal/reflectlite: skip TestMirrorWithReflect reflect package source is unavailable