Invoke ruff through PY_EXE and drop its duplicated excludes

runtests.sh called ruff as a bare executable on PATH while isort, black,
pylint and pytype all go through "${PY_EXE}" -m. The guard above it,
is_pip_installed ruff, tests importlib.util.find_spec using PY_EXE, so
the check interrogated one environment and the invocation ran whatever
ruff PATH happened to offer. In a clean virtualenv built per
CONTRIBUTING.md this makes ./runtests.sh --codeformat fail outright:

  ruff
  ./runtests.sh: line 598: ruff: command not found
  Check failed!

and where a system ruff does exist it silently wins over the pinned one.

The --exclude versioneer.py --exclude monai/_version.py flags are
dropped because [tool.ruff] extend-exclude now carries them, so they
apply however ruff is reached rather than only through this script.

--unsafe-fixes is left on the fix path as-is; making it symmetric with
the check path is a behaviour change and belongs on its own.

Signed-off-by: Hans Johnson <hans-johnson@uiowa.edu>

Author: hjmjohnson

runtests.sh

@@ -595,13 +595,13 @@ then
     then
         install_deps
     fi
-    ruff --version
+    ${cmdPrefix}"${PY_EXE}" -m ruff --version
 
     if [ $doRuffFix = true ]
     then
-        ruff check --fix --unsafe-fixes --exclude versioneer.py --exclude "monai/_version.py" "$homedir"
+        ${cmdPrefix}"${PY_EXE}" -m ruff check --fix --unsafe-fixes "$homedir"
     else
-        ruff check --exclude versioneer.py --exclude "monai/_version.py" "$homedir"
+        ${cmdPrefix}"${PY_EXE}" -m ruff check "$homedir"
     fi
 
     ruff_status=$?