vtk: Update to 9.6.1

Author: Dave-Allured

graphics/vtk/Portfile

@@ -2,7 +2,7 @@
 
 PortSystem          1.0
 PortGroup           cmake 1.1
-PortGroup           gitlab 1.0
+PortGroup           github 1.0
 PortGroup           legacysupport 1.1
 PortGroup           mpi 1.0
 PortGroup           muniversal 1.0
@@ -22,18 +22,19 @@ compiler.cxx_standard 2017
 # VTK 9.5.1+ Cmake says: Apple Clang 11.0 or later is required
 compiler.blacklist-append {clang < 1100}
 
-# Note, gitlab instance downloads distfile from gitlab tag in bz2 format,
-# not from the official VTK download page in gz format.
+# 2026 April 7: Must use Kitware Github mirror to avoid Anubis blockers.
+# Gitlab instance and VTK custom download page are both Anubis blocked.
+# On Github, only tags are mirrored, not releases.
 
-gitlab.instance     https://gitlab.kitware.com
-gitlab.setup        vtk vtk 9.5.2 v
-revision            1
+github.setup        Kitware vtk 9.6.1 v
+github.tarball_from archive
+revision            0
 categories          graphics devel
 license             BSD
 
-checksums           rmd160  06caa56eedf6a01d1e10bcc07ab2242e2dee1252 \
-                    sha256  a85763e3c040b6ae3139f1097339369456e1cc9d2aa6920f46da3709ddbe48e4 \
-                    size    40310394
+checksums           rmd160  1d40fead9fe3ac94c09a7ec7a4f6a460d7aeaec1 \
+                    sha256  a989db4ed5f7f35948f1f09b816dfcee3cc426f24828a3f94941c5eba8d4297c \
+                    size    54861772
 
 maintainers         {@Dave-Allured noaa.gov:dave.allured} \
                     openmaintainer
@@ -207,5 +208,5 @@ if {[mpi_variant_isset]} {
         -DVTK_USE_MPI:BOOL=ON
 }
 
-# Avoid release candidates
-gitlab.livecheck.regex  {([0-9.]+)}
+# Avoid release candidates.
+github.livecheck.regex  {([0-9.]+)}