Trac #31147: Add missing curly braces in latex of Kodaira symbol

{{{
sage: latex(EllipticCurve([0, -1, 0, -101781377,
-517919745247]).kodaira_symbol(2))
I_64^{*}
}}}

It should be `I_{64}^{*}`.

URL: https://trac.sagemath.org/31147
Reported by: roed
Ticket author(s): David Roe
Reviewer(s): Frédéric Chapoton, John Cremona, Samuel Lelièvre

Author: Release Manager

src/sage/schemes/elliptic_curves/kodaira_symbol.py

@@ -97,6 +97,11 @@ def __init__(self, symbol):
             I_n
             sage: KodairaSymbol_class('In')
             In
+
+        Check that :trac:`31147` is fixed::
+
+            sage: latex(KodairaSymbol_class(-14))
+            I_{10}^{*}
         """
         if not isinstance(symbol, str):
             n = Integer(symbol)
@@ -124,8 +129,8 @@ def __init__(self, symbol):
                 nu = n - 4
                 self._n = nu
                 self._roman = 1
-                self._str = 'I' + nu.str()
-                self._latex = 'I_{' + nu.str() + '}'
+                self._str = 'I%s' % nu
+                self._latex = 'I_{%s}' % nu
             elif n == -1:
                 self._roman = 1
                 self._n = 0
@@ -147,8 +152,8 @@ def __init__(self, symbol):
                 nu = -n - 4
                 self._roman = 1
                 self._n = nu
-                self._str = 'I' + nu.str() +'*'
-                self._latex = 'I_' + nu.str() + '^{*}'
+                self._str = 'I%s*' % nu
+                self._latex = 'I_{%s}^{*}' % nu
             self._starred = (n < 0)
             self._pari = n
             return