ci: Lock down to OIIO 2.5 for icc tests (#1799)

Background: Intel's icc is essentially discontinued and we think all
the renderers using OSL have moved on to the newer icx, but Alex Wells
still likes to sometime use icc for its better facilities for some
SIMD code generation sleuthing that he does. So we keep it in our CI
matrix to esure we don't break it for OSL until it is truly
unavoidable or he doesn't feel like he needs it anymore.

Some recent changes to OIIO's simd.h, from PR 4187 in that project,
seem to tweak what appears to be a compiler bug in icc -- bugs were
also noted in OIIO in the course of this PR and some workarounds were
put there just for icc to make OIIO's own tests pass. Well, once that
went in, OSL's CI tests for the icc case also started failing.  It's
only texture derivatives that are broken, and in a weird wy that
smells like a compiler icc bug with SIMD generation similar to what we
discovered on the OIIO side.

Like I said, this is a discontinued compiler that no major renderers
are still using, so it doesn't seem worth tracking it down any further
to find a true fix. So let's just lock that one test case down to OIIO
2.5 (the current release) to avoid the changes that will eventually be
in OIIO 2.6/3.0 and hope that we fully retire icc before OIIO 2.5 is
no longer supported by OSL.

Signed-off-by: Larry Gritz <[email protected]>

Author: lgritz

.github/workflows/ci.yml

@@ -117,7 +117,14 @@ jobs:
             cxx_compiler: icpc
             cxx_std: 17
             fmt_ver: 7.1.3
-            openimageio_ver: master
+            openimageio_ver: release
+            # Changes to OIIO's simd.h starting in commit 68666db9 (from PR
+            # #4187) seem to trigger compiler bugs in icc and generate wrong
+            # SIMD code. It's probably not worth tracking down for just this
+            # obsolete compiler. Just lock down to OIIO 2.5 for icc builds to
+            # avoid the problem.
+            # openimageio_ver: e41ac03c0b21  # works
+            # openimageio_ver: 68666db994d5 # broken
             python_ver: 3.9
             pybind11_ver: v2.9.0
             # simd: avx2,f16c