Fix wio-e5-mini_repeater build

[sefinek]

The wio-e5-mini_repeater build fails with:

.pio/libdeps/wio-e5-mini_repeater/RadioLib/src/hal/Stm32duino/Stm32wlHal.cpp:15:10: fatal error: SubGhz.h: No such file or directory

   15 | #include <SubGhz.h>
      |          ^~~~~~~~~~
compilation terminated.
*** [.pio/build/wio-e5-mini_repeater/libe5e/RadioLib/hal/Stm32duino/Stm32wlHal.cpp.o] Error 1
========================= [FAILED] Took 75.80 seconds =========================

Cause

jgromes/RadioLib@^7.6.0 pulls the latest 7.7.x (7.7.1). Since 7.7.0, Stm32wlHal.cpp includes #include <SubGhz.h> - a header that is likely unavailable in the pinned STM32 core 2.10.1.

Fix

Pin to 7.6.0.

- jgromes/RadioLib @ ^7.6.0
+ jgromes/RadioLib @ 7.6.0

Verification

The full build PASSED.

Before	After