nixos/munge: run munge as user munge instead of root.

[markuskowa]

Motivation for this change

The munge daemon does not require root privileges.

Fixes #41092

Things done

• Added a note in release notes (incompatibilities)
• Adapt slurm test
• Change user to munge in service.munge

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
  The slurm test requires munge to run and thus serves also as a test for munge.
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.

---

[xeji]

@GrahamcOfBorg test slurm

[GrahamcOfBorg]

Failure on x86_64-linux (full log)

Attempted: tests.slurm

Partial log (click to expand)

cleaning up
killing submit (pid 593)
killing node2 (pid 605)
killing node1 (pid 617)
killing node3 (pid 629)
killing control (pid 641)
vde_switch: EOF on stdin, cleaning up and exiting
vde_switch: Could not remove ctl dir '/build/vde1.ctl': Directory not empty
builder for '/nix/store/3ckhn2yaakzq16hbljangai01incn4cs-vm-test-run-slurm.drv' failed with exit code 255
error: build of '/nix/store/3ckhn2yaakzq16hbljangai01incn4cs-vm-test-run-slurm.drv' failed

[xeji]

Test failure is unrelated, test succeeds locally

[GrahamcOfBorg]

Success on aarch64-linux (full log)

Attempted: tests.slurm

Partial log (click to expand)

test script finished in 28.03s
cleaning up
killing submit (pid 627)
killing node2 (pid 640)
killing control (pid 653)
killing node3 (pid 666)
killing node1 (pid 679)
vde_switch: EOF on stdin, cleaning up and exiting
vde_switch: Could not remove ctl dir '/build/vde1.ctl': Directory not empty
/nix/store/wdb8yd7z4isk9np1vr9qmns90ax0fgy0-vm-test-run-slurm