add SPI dependency

I don't know why this is needed on my local setup.
I've cleaned everything multiple times, but it still
complained about a missing SPI.h.
The github action worked without it, but this may be
due to some caching.
Hopefully it will not break anything.

platformio.ini

@@ -15,12 +15,13 @@
     platform = espressif32
     framework = arduino
     lib_deps = 
-	    https://github.com/tzapu/WiFiManager.git
-	    https://github.com/me-no-dev/ESPAsyncWebServer.git
-	    https://github.com/eModbus/eModbus.git#ed343224827600409e4d57e77e60b73ff9c22f1a
+        https://github.com/tzapu/WiFiManager.git
+        https://github.com/me-no-dev/ESPAsyncWebServer.git
+        https://github.com/eModbus/eModbus.git#ed343224827600409e4d57e77e60b73ff9c22f1a
+        SPI
     build_flags = -Wall -Werror -DLOG_LEVEL=LOG_LEVEL_DEBUG
     monitor_speed = 115200
-    
+
 [env:esp32release]
     board = esp32dev
     build_flags = ${env.build_flags}
@@ -34,7 +35,7 @@
     build_flags = ${env.build_flags} -DRX_PIN=14 -DTX_PIN=5
     upload_port = COM9
     monitor_port = COM9
-    
+
 [env:d1mini]
     board = wemos_d1_mini32
     build_flags = ${env.build_flags}