build: align rustc version warning with minimum requirement

Raise the rustc warning threshold to 1.88 to match BUILDING.md and
deps/crates/Cargo.toml. Keep the cargo threshold at 1.86.

Assisted-by: Codex
Signed-off-by: inoway46 <inoueyuya416@gmail.com>

Author: inoway46

configure.py

@@ -1671,7 +1671,7 @@ def check_compiler(o):
   if not options.v8_disable_temporal_support and not options.shared_temporal_capi:
     # Minimum cargo and rustc versions should match values in BUILDING.md.
     min_cargo_ver_tuple = (1, 86)
-    min_rustc_ver_tuple = (1, 86)
+    min_rustc_ver_tuple = (1, 88)
     cargo = os.environ.get('CARGO', 'cargo')
     cargo_ver = get_cargo_version(cargo)
     print_verbose(f'Detected cargo (CARGO={cargo}): {cargo_ver}')