ci: downgrade Coinkite sim builder and tests to Ubuntu 22.04

Build failure on ubuntu-latest:

```
../py/stackctrl.c: In function ‘mp_stack_ctrl_init’:
../py/stackctrl.c:32:32: error: storing the address of local variable ‘stack_dummy’ in ‘mp_state_ctx.thread.stack_top’ [-Werror=dangling-pointer=]
   32 |     MP_STATE_THREAD(stack_top) = (char *)&stack_dummy;
../py/stackctrl.c:31:18: note: ‘stack_dummy’ declared here
   31 |     volatile int stack_dummy;
      |                  ^~~~~~~~~~~
In file included from ../py/runtime.h:29,
                 from ../py/stackctrl.c:27:
../py/mpstate.h:282:23: note: ‘mp_state_ctx’ declared here
  282 | extern mp_state_ctx_t mp_state_ctx;
      |                       ^~~~~~~~~~~~
cc1: all warnings being treated as errors
make: *** [../py/mkrules.mk:77: build/py/stackctrl.o] Error 1
```

Test failure (after downgrading build sim):

```
 File "/github/home/.cache/pypoetry/virtualenvs/hwi-crEDFiR--py3.9/lib/python3.9/site-packages/sdl2/dll.py", line 362, in <module>
    dll = DLL("SDL2", ["SDL2", "SDL2-2.0", "SDL2-2.0.0"], os.getenv("PYSDL2_DLL_PATH"))
  File "/github/home/.cache/pypoetry/virtualenvs/hwi-crEDFiR--py3.9/lib/python3.9/site-packages/sdl2/dll.py", line 253, in __init__
    raise RuntimeError("could not find any library for %s (%s)" %
RuntimeError: could not find any library for SDL2 (PYSDL2_DLL_PATH: unset)
```

https://github.com/bitcoin-core/HWI/actions/runs/16466809973/job/46548656293?pr=795

Author: Sjors

.github/workflows/ci.yml

@@ -159,7 +159,7 @@ jobs:
 
   sim-builder-coldcard:
     name: Coldcard sim builder
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
 
     strategy:
       fail-fast: false
@@ -374,7 +374,7 @@ jobs:
 
   test-coldcard:
       name: Python ${{ matrix.python-version }} ${{ matrix.device }} ${{ matrix.interface }}
-      runs-on: ubuntu-latest
+      runs-on: ubuntu-22.04
       needs: [ sim-builder-coldcard, bitcoind-builder ]
       timeout-minutes: 45