internal/lsp: add temporary file to fix bug with tip go

There is a problem with this test failing in module mode only with the
tip of the go tree. Adding this file changes it from a pure overlay package
to one that has an extra file, which fixes it for now.

updates golang/go#33125

Change-Id: I87dae0b44691246a1f79df454afb190f944cc886
Reviewed-on: https://go-review.googlesource.com/c/tools/+/186259
Run-TryBot: Ian Cottrell <iancottrell@google.com>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/internal/lsp/testdata/nodisk/nodisk_exists.go b/internal/lsp/testdata/nodisk/nodisk_exists.go
new file mode 100644
index 0000000..fbccebd
--- /dev/null
+++ b/internal/lsp/testdata/nodisk/nodisk_exists.go
@@ -0,0 +1,3 @@
+package nodisk
+
+//TODO: remove this file when https://github.com/golang/go/issues/33125 is fixed.
\ No newline at end of file