gh-149521: Do not update last_profiled_frame if it's not changed

[maurycy]

With the patch applied, the number of process_vm_writev for this script:

def f():
    x = 0
    while True:
        x += 1
f()

went from 118241 to 2:

2026-05-07T23:57:57.377240168+0000 maurycy@weiss /home/maurycy/cpython (remote-debugging-last-profiled-frame 1a07c4a*) # ./python.exe /tmp/spin.py & TGT=$!
sleep 0.5
strace -c -f -e trace=process_vm_writev,process_vm_readv,pwritev,pwritev2 \
  ./python.exe -m profiling.sampling attach -r 100khz -d 30 \
  --pstats -o /tmp/out.pstats $TGT
kill $TGT; wait 2>/dev/null
[1] 136124
Captured 158384 samples in 30.00 seconds
Sample rate: 5279.46 samples/sec
Error rate: 0.00
Warning: missed 2841621 samples from the expected total of 3000005 (94.72%)
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ------------------
100.00    1.180278           2    475164           process_vm_readv
  0.00    0.000007           3         2           process_vm_writev
------ ----------- ----------- --------- --------- ------------------
100.00    1.180285           2    475166           total
[1]  + terminated  ./python.exe /tmp/spin.py

Note how process_vm_readv went up!

Closes #149521

• Issue: _remote_debugging: no need to update last_profiled_frame if no change #149521

[pablogsal]

Excellent catch!