cmd/compile/internal/syntax: rename test file to match issue

Follow-up on CL 565518 which addressed issue #65790 but added
testdata/issue65970.go instead of testdata/issue65790.go.
Rename that file to match the issue.

For #65790.

Change-Id: I647c297286355137fa950fb6722e31ae4340393b
Reviewed-on: https://go-review.googlesource.com/c/go/+/567875
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

diff --git a/src/cmd/compile/internal/syntax/testdata/issue65970.go b/src/cmd/compile/internal/syntax/testdata/issue65790.go
similarity index 100%
rename from src/cmd/compile/internal/syntax/testdata/issue65970.go
rename to src/cmd/compile/internal/syntax/testdata/issue65790.go