solfege: fix build with texinfo 6.7

makeinfo seems right to fail when input encoding is not declared and is not UTF-8.

texinfo was updated in #95910.

pkgs/misc/solfege/default.nix

@@ -15,6 +15,7 @@ buildPythonApplication rec {
   patches = [
     ./css.patch
     ./menubar.patch
+    ./texinfo.patch
     ./webbrowser.patch
   ];
 

pkgs/misc/solfege/texinfo.patch

@@ -0,0 +1,20 @@
+Fix build with texinfo 6.7. Otherwise
+
+    makeinfo -I topdocs --no-split --no-headers --output AUTHORS topdocs/AUTHORS.texi
+
+fails with
+
+    utf8 "\xC1" does not map to Unicode at /nix/store/...-texinfo-6.7/share/texinfo/Texinfo/ParserNonXS.pm line 1796, <FH> line 38.
+
+--- a/topdocs/AUTHORS.texi
++++ b/topdocs/AUTHORS.texi
+@@ -1,2 +1,3 @@
+ \input texinfo
++@documentencoding ISO-8859-1
+ @setfilename AUTHORS.info
+--- a/topdocs/README.texi
++++ b/topdocs/README.texi
+@@ -1,2 +1,3 @@
+ \input texinfo
++@documentencoding ISO-8859-1
+ @setfilename README.info