Allow tab after key name in TOML.parse (#51622)

Fixes JuliaLang/TOML.jl#52

Author: jaakkor2

base/toml_parser.jl

@@ -611,7 +611,7 @@ function _parse_key(l::Parser)
     else
         set_marker!(l)
         if accept_batch(l, isvalid_barekey_char)
-            if !(peek(l) == '.' || peek(l) == ' ' || peek(l) == ']' || peek(l) == '=')
+            if !(peek(l) == '.' || iswhitespace(peek(l)) || peek(l) == ']' || peek(l) == '=')
                 c = eat_char(l)
                 return ParserError(ErrInvalidBareKeyCharacter, c)
             end

stdlib/TOML/test/parse.jl

@@ -14,6 +14,7 @@ using TOML: ParserError
           TOML.parse(IOBuffer(str)) ==
           TOML.parse(p, str) == TOML.parse(p, SubString(str)) ==
           TOML.parse(p, IOBuffer(str)) == dict
+    @test TOML.parse("a\t=1") == dict
     @test_throws ParserError TOML.parse(invalid_str)
     @test_throws ParserError TOML.parse(SubString(invalid_str))
     @test_throws ParserError TOML.parse(IOBuffer(invalid_str))