fix(health): hard fail on invalid "python-*" bin #35382

Problem:
Scripts named with 'python-…' prefix may not be valid python bins. If
such a script is found in a venv, the Python healthcheck fails hard.

    .venv/python-argcomplete-check-easy-install-script
    .venv/bin/python3.13
    .venv/bin/python

Solution:
- Discard known false-positives such as `python-argcomplete*`.
- Call `health.warn()` instead of `assert()` in `python_exepath()`.

Co-authored-by: Justin M. Keyes <justinkz@gmail.com>

runtime/lua/vim/provider/health.lua

@@ -364,8 +364,14 @@ end
 
 -- Resolves Python executable path by invoking and checking `sys.executable`.
 local function python_exepath(invocation)
+  if invocation == '' or invocation == nil then
+    return nil
+  end
   local p = vim.system({ invocation, '-c', 'import sys; sys.stdout.write(sys.executable)' }):wait()
-  assert(p.code == 0, p.stderr)
+  if p.code ~= 0 then
+    health.warn(p.stderr)
+    return nil
+  end
   return vim.fs.normalize(vim.trim(p.stdout))
 end
 
@@ -790,13 +796,14 @@ local function python()
   --- @param v string
   venv_bins = vim.tbl_filter(function(v)
     -- XXX: Remove irrelevant executables found in bin/.
-    return not v:match('python.*%-config')
+    return not v:match('python.*%-config') and not v:match('python%-argcomplete')
   end, venv_bins)
   if vim.tbl_count(venv_bins) > 0 then
     for _, venv_bin in pairs(venv_bins) do
       venv_bin = vim.fs.normalize(venv_bin)
       local py_bin_basename = vim.fs.basename(venv_bin)
       local nvim_py_bin = python_exepath(vim.fn.exepath(py_bin_basename))
+      if nvim_py_bin then
         local subshell_py_bin = python_exepath(py_bin_basename)
         if venv_bin ~= nvim_py_bin then
           errors[#errors + 1] = '$PATH yields this '
@@ -821,6 +828,7 @@ local function python()
           hints[hint] = true
         end
       end
+    end
   else
     errors[#errors + 1] = 'no Python executables found in the virtualenv '
       .. bin_dir
@@ -849,6 +857,7 @@ local function python()
       msgs[#msgs + 1] = msg
       msgs[#msgs + 1] = conj
       msgs[#msgs + 1] = err
+      msgs[#msgs + 1] = '\n'
       conj = '\nAnd '
     end
     msgs[#msgs + 1] = '\nSo invoking Python may lead to unexpected results.'