ci(arm): set PATH in the Rocky 10 container so run steps find sh

The community rockylinux/rockylinux:10 image omits PATH from its image
config, unlike the old Docker Official arm64v8/rockylinux:9. GitHub Actions
derives each run step's PATH from that config, so with no PATH the shell
exec (docker exec ... sh -e {0}) fails with exit 127, 'exec: sh: not found'
— it broke before any build logic ran. Restore a standard PATH via the
container env; the runner still layers GITHUB_PATH additions (uv, cargo)
on top.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.github/workflows/build_rocky_arm.yml

@@ -10,7 +10,15 @@ jobs:
     # against glibc 2.38, which Rocky 9 (glibc 2.34) can't run (moc fails to
     # load). The legacy arm64v8/rockylinux Docker image stopped at 9; Rocky 10
     # is published under the rockylinux/rockylinux namespace.
-    container: rockylinux/rockylinux:10
+    container:
+      image: rockylinux/rockylinux:10
+      # The community rockylinux image omits PATH from its config (the old
+      # Docker Official arm64v8/rockylinux set it), so GitHub Actions `run:`
+      # steps fail with `exec: "sh": not found` — docker exec has no /usr/bin
+      # to resolve the shell. Restore a standard PATH; GITHUB_PATH prepends
+      # (uv, cargo) are still layered on top by the runner.
+      env:
+        PATH: /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
 
     steps:
       - name: Set up uv