Fix Makefile

- Because PYTHON_INTERPRETER is declared afterwards, it'll result in an empty value which would lead to some files being installed in the wrong path or the wrong path being used when executing the entry point.

Makefile.in

@@ -1,5 +1,9 @@
 PROJECT := umu-launcher
 
+# Define the interpreters to use to prevent shebang complaints
+PYTHON_INTERPRETER = /usr/bin/python3
+SHELL_INTERPRETER = /usr/bin/sh
+
 # If this is changed to umu (uppercase), `uninstall` target will also remove the SLR directory
 INSTALLDIR ?= umu
 
@@ -16,10 +20,6 @@ DESTDIR ?=
 USERINSTALL ?= xfalse
 FLATPAK ?= xfalse
 
-# Define the interpreters to use to prevent shebang complaints
-PYTHON_INTERPRETER = /usr/bin/python3
-SHELL_INTERPRETER = /usr/bin/sh
-
 .PHONY: all
 ifeq ($(FLATPAK), xtrue)
 all: version umu umu-launcher