🐛 Fix thermistor 14 & 60 constexprness (#26499)

Author: ellensp

Marlin/src/module/thermistor/thermistor_14.h

@@ -22,7 +22,7 @@
 #pragma once
 
 // R25 = 100 kOhm, beta25 = 4092 K, 4.7 kOhm pull-up, bed thermistor
-const temp_entry_t temptable_14[] PROGMEM = {
+constexpr temp_entry_t temptable_14[] PROGMEM = {
   { OV(  23), 275 },
   { OV(  25), 270 },
   { OV(  27), 265 },

Marlin/src/module/thermistor/thermistor_68.h

@@ -24,7 +24,7 @@
 #define REVERSE_TEMP_SENSOR_RANGE_68 1
 
 // PT100 amplifier board from Dyze Design
-const temp_entry_t temptable_68[] PROGMEM = {
+constexpr temp_entry_t temptable_68[] PROGMEM = {
   { OV(273), 0   },
   { OV(294), 20  },
   { OV(315), 40  },