gh-126529: Update devguide links to relative filenames in InternalDocs (#126530)

Update devguide links to relative filenames in InternalDocs/parser.md
and InternalDocs/compiler.md.

Author: valerii-software

InternalDocs/compiler.md

@@ -42,10 +42,10 @@ The definitions for literal tokens (such as `:`, numbers, etc.) can be found in
 
 See Also:
 
-* [Guide to the parser](https://devguide.python.org/internals/parser/index.html)
+* [Guide to the parser](parser.md)
   for a detailed description of the parser.
 
-* [Changing CPython’s grammar](https://devguide.python.org/developer-workflow/grammar/#grammar)
+* [Changing CPython’s grammar](changing_grammar.md)
   for a detailed description of the grammar.
 
 

InternalDocs/parser.md

@@ -17,7 +17,7 @@ Therefore, changes to the Python language are made by modifying the
 [grammar file](../Grammar/python.gram).
 Developers rarely need to modify the generator itself.
 
-See [Changing CPython's grammar](./changing_grammar.md)
+See [Changing CPython's grammar](changing_grammar.md)
 for a detailed description of the grammar and the process for changing it.
 
 How PEG parsers work