python313Packages.tkinter: fix nix-shell usage

$NIX_BUILD_TOP was used inconsistently and the name of the Python source directory was assumed to have a certain pattern. These changes make the build work better in a nix-shell.

pkgs/development/python-modules/tkinter/default.nix

@@ -20,12 +20,14 @@ buildPythonPackage {
   src = python.src;
 
   prePatch = ''
-    mkdir $NIX_BUILD_TOP/tkinter
+    python_src=$PWD
+    tkinter_src=$PWD/../tkinter
+    mkdir -p "$tkinter_src"
 
     # copy the module bits and pieces from the python source
-    cp -v  Modules/{_tkinter.c,tkinter.h} ../tkinter/
-    cp -rv Modules/clinic ../tkinter/
-    cp -rv Lib/tkinter ../tkinter/
+    cp -v  Modules/{_tkinter.c,tkinter.h} "$tkinter_src"
+    cp -rv Modules/clinic "$tkinter_src"
+    cp -rv Lib/tkinter "$tkinter_src"
 
     # install our custom pyproject.toml
     cp ${
@@ -33,11 +35,11 @@ buildPythonPackage {
         python_version = python.version;
         python_internal_dir = "${python}/include/${python.libPrefix}/internal";
       }
-    } $NIX_BUILD_TOP/tkinter/pyproject.toml
+    } "$tkinter_src"/pyproject.toml
 
   ''
   + lib.optionalString (pythonOlder "3.13") ''
-    substituteInPlace "$NIX_BUILD_TOP/tkinter/tkinter/tix.py" --replace-fail \
+    substituteInPlace "$tkinter_src/tkinter/tix.py" --replace-fail \
       "os.environ.get('TIX_LIBRARY')" \
       "os.environ.get('TIX_LIBRARY') or '${tclPackages.tix}/lib'"
   '';
@@ -46,7 +48,7 @@ buildPythonPackage {
   patches = lib.optional (pythonOlder "3.12") ./fix-ttk-notebook-test.patch;
 
   preConfigure = ''
-    pushd $NIX_BUILD_TOP/tkinter
+    cd "$tkinter_src"
   '';
 
   build-system = [ setuptools ];
@@ -72,7 +74,7 @@ buildPythonPackage {
   nativeCheckInputs = lib.optional stdenv.hostPlatform.isLinux xvfb-run;
 
   preCheck = ''
-    cd $NIX_BUILD_TOP/Python-*/Lib
+    cd "$python_src"/Lib
     export HOME=$TMPDIR
   '';