fix: cite the gam4980 fork at the revision pinned

The refs described upstream's libretro.c while source_commit named the fork, where the loader moved to src/ and a missing ROM now shuts the core down cleanly. A bump no longer advances a pin no ref resolves in.

emulators/gam4980.yml

@@ -16,14 +16,13 @@ systems:
 # Original code from https://codeberg.org/iyzsong/gam4980, based on the
 # BA4988 BBK simulator by Wuyun. Uses a 6502-based CPU with banked ROM access.
 #
-# ROM loading (libretro.c:692-760, sys_init):
+# ROM loading (src/libretro.c:707-746, sys_init):
 #   Opens romdir/8.BIN and reads 0x200000 bytes (2 MB) into sys.rom_8 (font ROM).
 #   Opens romdir/E.BIN and reads 0x200000 bytes (2 MB) into sys.rom_e (OS ROM).
-#   The upstream has error handling (error_msg + RETRO_ENVIRONMENT_SHUTDOWN on
-#   missing files). The fork (ThisBoringWorld) removed these checks -- crashes
-#   on missing files.
+#   A missing file shows "GAM4980: Missing 8.BIN" (or E.BIN) and the core
+#   shuts down through RETRO_ENVIRONMENT_SHUTDOWN.
 #
-# Memory map (libretro.c:109-110, 300-305):
+# Memory map (src/libretro.c:109-110, 302-305):
 #   0x800000-0x9FFFFF  rom_8 (font ROM, 8.BIN)
 #   0xE00000-0xFFFFFF  rom_e (OS ROM, E.BIN)
 #
@@ -42,19 +41,19 @@ files:
     required: true
     system: bbk-longman-4980
     note: "Font ROM (2 MB). Loaded at 0x800000."
-    source_ref: "libretro.c:716-718"
+    source_ref: "src/libretro.c:730-737"
 
   - name: "gam4980/E.BIN"
     size: 2097152
     required: true
     system: bbk-longman-4980
     note: "OS ROM (2 MB). Loaded at 0xE00000."
-    source_ref: "libretro.c:720-722"
+    source_ref: "src/libretro.c:739-746"
 
 platform_details:
   bios_mapping:
     target: "0x800000-0x9FFFFF (font), 0xE00000-0xFFFFFF (OS) in banked address space"
-    source_ref: "libretro.c:109-110, 300-305"
+    source_ref: "src/libretro.c:109-110, 302-305"
     note: |
       sys.rom_8 and sys.rom_e are flat 2 MB arrays. The CPU accesses them
       through bank-switched memory (PA() macro resolves virtual to physical
@@ -62,7 +61,7 @@ platform_details:
       the banking system.
 
   load_path:
-    source_ref: "libretro.c:1173-1175"
+    source_ref: "src/libretro.c:1193-1197"
     note: |
       retro_init() builds the path as {system_directory}/gam4980/ and
       passes it to sys_init(). Files must be named exactly 8.BIN and