Fix DaynaPORT build - decrease prefetch buffer

The Pico DaynaPORT build failed to build because it ran out of SRAM.
Decreasing the prefetch buffer by 512B fixed the build issue.

Also updated the GitHub workflow to the new version.

.github/workflows/firmware_build.yml

@@ -14,7 +14,7 @@ jobs:
     
     steps:
       - name: Check out code from GitHub
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           path: ZuluSCSI
           fetch-depth: "0"

platformio.ini

@@ -153,8 +153,8 @@ debug_build_flags =
     -DLOGBUFSIZE=4096
     -DPREFETCH_BUFFER_SIZE=0
     -DSCSI2SD_BUFFER_SIZE=57344
-    ; This controls the depth of 2 x NETWORK_PACKET_MAX_SIZE (1520 bytes)
-    ; For example a queue size of 10 would be 10 x 2 x 1520 = 30400 bytes
+    ; This controls the depth NETWORK_PACKET_MAX_SIZE (1520 bytes)
+    ; For example a queue size of 10 would be 10 x 1520 = 30400 bytes
     -DNETWORK_PACKET_QUEUE_SIZE=10
 
 lib_deps =
@@ -176,7 +176,7 @@ build_flags =
     -DZULUSCSI_DAYNAPORT
 ; These take a large portion of the SRAM and can be adjusted
     -DLOGBUFSIZE=8192
-    -DPREFETCH_BUFFER_SIZE=5632
+    -DPREFETCH_BUFFER_SIZE=5120
     -DSCSI2SD_BUFFER_SIZE=57344
     ; This controls the depth of NETWORK_PACKET_MAX_SIZE (1520 bytes)
     ; For example a queue size of 10 would be 10 x 1520 = 15200 bytes