fix(docker): pass --shm-size so Unity 6.6+ builds work (backport)

Unity 6.6+ editors request 1GiB of shared memory and hard-fail with
"Insufficient shared memory available - if using Docker, please run the
container with --shm-size=1025M" against Docker's 64m default.

This action never passed --shm-size at all and exposed no input to work
around it, so affected users had no escape hatch whatsoever. Reported as
#840 (closed as not-planned) and again on Discord against Unity
6000.6.0f1.

Backport of the fix already merged into game-ci/cli (#239), which owns
this code going forward. Adds the dockerShmSize input, the
BuildParameters field, and the flag on both the Linux and Windows
commands, defaulting to 1025m - the value unity-test-runner has always
passed. --shm-size caps a tmpfs rather than preallocating memory, so the
default costs nothing for editors that don't need it. "0"/"none" opts
back out to Docker's own default.

Co-Authored-By: Claude Opus 5 <[email protected]>

action.yml

@@ -128,6 +128,13 @@ inputs:
     required: false
     default: ''
     description: 'Number of CPU cores to assign the docker container. Defaults to all available cores on all platforms.'
+  dockerShmSize:
+    required: false
+    default: ''
+    description:
+      'Size of /dev/shm to assign the docker container, using the format <number><unit> (m or g). Unity 6.6+ editors
+      request 1GiB of shared memory and fail with "Insufficient shared memory available" against Docker''s 64m
+      default. Defaults to 1025m; set to "0" or "none" to use Docker''s own default.'
   dockerMemoryLimit:
     required: false
     default: ''