Bump software version to 2.6

Update kSoftwareVersion from 2.5 to 2.6 in firmware-template-gd32/include/software_version.h to reflect the new release.

Author: vanvught

firmware-template-gd32/include/software_version.h

@@ -26,6 +26,6 @@
 #ifndef SOFTWARE_VERSION_H_
 #define SOFTWARE_VERSION_H_
 
-constexpr char kSoftwareVersion[] = "2.5";
+constexpr char kSoftwareVersion[] = "2.6";
 
 #endif // SOFTWARE_VERSION_H_