build: enable lintlua for test/unit/ dir #26396

Problem:
Not all Lua code is checked by stylua. Automating code-style is an
important mechanism for reducing time spent on accidental
(non-essential) complexity.

Solution:
- Enable lintlua for `test/unit/` directory.
- TODO: only `test/functional/` remains unchecked.

previous: 45fe4d11ad
previous: 517f0cc634

test/unit/os/env_spec.lua

@@ -62,7 +62,7 @@ describe('env.c', function()
       eq('non-empty', os.getenv(name))
     end)
 
-    itp("`overwrite` behavior", function()
+    itp('`overwrite` behavior', function()
       local name = 'NVIM_UNIT_TEST_SETENV_2N'
       local value = 'NVIM_UNIT_TEST_SETENV_2V'
       local value_updated = 'NVIM_UNIT_TEST_SETENV_2V_UPDATED'
@@ -79,7 +79,7 @@ describe('env.c', function()
     itp('appends :/foo/bar to $PATH', function()
       local original_path = os.getenv('PATH')
       eq(true, cimp.os_setenv_append_path(to_cstr('/foo/bar/baz.exe')))
-      eq(original_path..':/foo/bar', os.getenv('PATH'))
+      eq(original_path .. ':/foo/bar', os.getenv('PATH'))
     end)
 
     itp('avoids redundant separator when appending to $PATH #7377', function()
@@ -166,7 +166,7 @@ describe('env.c', function()
       local test_value = 'NVIM_UNIT_TEST_GETENVNAME_AT_INDEX_1V'
       os_setenv(test_name, test_value, 1)
       local i = 0
-      local names = { }
+      local names = {}
       local found_name = false
       local name = cimp.os_getenvname_at_index(i)
       while name ~= NULL do
@@ -245,7 +245,7 @@ describe('env.c', function()
       local input = '~/foo ~ foo'
       local homedir = cstr(255, '')
       cimp.expand_env_esc(to_cstr('~'), homedir, 255, false, true, NULL)
-      local output_expected = ffi.string(homedir) .. "/foo ~ foo"
+      local output_expected = ffi.string(homedir) .. '/foo ~ foo'
       local output = cstr(255, '')
       cimp.expand_env_esc(to_cstr(input), output, 255, false, true, NULL)
       eq(ffi.string(output), ffi.string(output_expected))
@@ -256,7 +256,7 @@ describe('env.c', function()
       local dst = cstr(255, '')
       cimp.expand_env_esc(to_cstr('~'), dst, 255, false, true, NULL)
       local homedir = ffi.string(dst)
-      local output_expected = homedir .. "/foo " .. homedir .. " foo"
+      local output_expected = homedir .. '/foo ' .. homedir .. ' foo'
       local output = cstr(255, '')
       cimp.expand_env_esc(input, output, 255, false, false, NULL)
       eq(output_expected, ffi.string(output))
@@ -267,8 +267,9 @@ describe('env.c', function()
       cimp.os_get_username(name_out, 100)
       local curuser = ffi.string(name_out)
 
-      local src = to_cstr("~"..curuser.."/Vcs/django-rest-framework/rest_framework/renderers.py")
-      local dst = cstr(256, "~"..curuser)
+      local src =
+        to_cstr('~' .. curuser .. '/Vcs/django-rest-framework/rest_framework/renderers.py')
+      local dst = cstr(256, '~' .. curuser)
       cimp.expand_env_esc(src, dst, 256, false, false, NULL)
       local len = string.len(ffi.string(dst))
       assert.True(len > 56)
@@ -283,7 +284,7 @@ describe('env.c', function()
       cimp.expand_env_esc(input, output, 5, false, true, NULL)
       -- Make sure the first few characters are copied properly and that there is a
       -- terminating null character
-      for i=0,3 do
+      for i = 0, 3 do
         eq(input[i], output[i])
       end
       eq(0, output[4])
@@ -304,7 +305,7 @@ describe('env.c', function()
       -- terminating null character
       -- expand_env_esc SHOULD NOT expand the variable if there is not enough space to
       -- contain the result
-      for i=0,3 do
+      for i = 0, 3 do
         eq(output[i], input[i])
       end
       eq(output[4], 0)