security/gpgme-cpp: Fix constness

The 1.15.0 release of gpgme-cpp adds a `Signature::operator<` which is missing
a const. In 6a6d2a27648, Signature got an operator< . This is used in
*security/libkleo*, for instance, to sort the signatures for display.

The build failure looks like this (trimmed for brevity, on 13-):

===
/usr/include/c++/v1/algorithm:715:71: error: invalid operands to binary
expression ('const GpgME::UserID::Signature' and 'const
GpgME::UserID::Signature')
    bool operator()(const _T1& __x, const _T1& __y) const {return __x < __y;}

/wrkdirs/usr/ports/security/libkleo/work/libkleo-20.12.0/src/models/
useridlistmodel.cpp:203:14: note: in instantiation of function template
specialization 'std::__1::sort<GpgME::UserID::Signature>' requested here
        std::sort(sigs.begin(), sigs.end());
===

PR:		252283
Submitted by:	adridg

security/gpgme-cpp/Makefile

@@ -1,6 +1,6 @@
 # $FreeBSD$
 
-PORTREVISION=	0
+PORTREVISION=	1
 PKGNAMESUFFIX=	-${SLAVEPORT}
 
 MAINTAINER=	jhale@FreeBSD.org

security/gpgme/files/patch-git-key.h

@@ -0,0 +1,29 @@
+The operator< should be const, so it can be applied to const Signatures.
+This fixes a build failure in security/libkleo.
+
+diff --git lang/cpp/src/key.cpp lang/cpp/src/key.cpp
+index e536d080..7411e9e4 100644
+--- lang/cpp/src/key.cpp
++++ lang/cpp/src/key.cpp
+@@ -865,7 +865,7 @@ UserID::Signature::Signature(const shared_gpgme_key_t &k, gpgme_user_id_t u, gpg
+ {
+ }
+ 
+-bool UserID::Signature::operator<(const Signature &other)
++bool UserID::Signature::operator<(const Signature &other) const
+ {
+     // based on cmp_signodes() in g10/keylist.c
+ 
+diff --git lang/cpp/src/key.h lang/cpp/src/key.h
+index a7931672..57001a03 100644
+--- lang/cpp/src/key.h
++++ lang/cpp/src/key.h
+@@ -468,7 +468,7 @@ public:
+     }
+ 
+     /*! Defines a canonical sort order for signatures of the same user ID. */
+-    bool operator<(const Signature &other);
++    bool operator<(const Signature &other) const;
+ 
+     bool isNull() const
+     {