Replace all known shas with just the latest, drop Python 3.9 (#64)

The first two versions were using the `max` package, and the third was
deleted since it was `mojo>1.0.0`, so now only versions <1.0.0 exist.
Removing those 3 and adding the latest to fix CI.

Python 3.9 support was also dropped, so remove that to fix a failing
test.

Author: Ahajha

MODULE.bazel

@@ -19,7 +19,6 @@ register_toolchains("@mojo_toolchains//...", "@mojo_gpu_toolchains//...")
 _DEFAULT_PYTHON_VERSION = "3.12"
 
 _PYTHON_VERSIONS = [
-    "3.9",
     "3.10",
     "3.11",
     "3.12",

mojo/extensions.bzl

@@ -4,22 +4,12 @@ load("//mojo:mojo_host_platform.bzl", "mojo_host_platform")
 load("//mojo/private:mojo_gpu_toolchains_repository.bzl", "mojo_gpu_toolchains_repository")
 
 _PLATFORMS = ["linux_aarch64", "linux_x86_64", "macos_arm64"]
-_DEFAULT_VERSION = "25.6.0.dev2025082505"
+_DEFAULT_VERSION = "0.25.7.0.dev2025101005"
 _KNOWN_SHAS = {
-    "25.4.0.dev2025050902": {
-        "linux_aarch64": "d52c67f245575397d8176010d27bd12e76cde297ed8ee7f07dcc73fe48955508",
-        "linux_x86_64": "69898a4ffb328489e5c7c1c7e0cba37cd64dd0fa87b4a98501b3562dc89f2695",
-        "macos_arm64": "8856745cab1cb88fbba174afb9784cbdda865c8a4e4db5693750efefe7505160",
-    },
-    "25.5.0.dev2025062305": {
-        "linux_aarch64": "7b516b9ef485cc25f981d438bba974108dc115509d17f58431866bde8f962043",
-        "linux_x86_64": "51302b87d8d83891762877be0bf73fffbf196a47246be339e818c4b3480e1ac4",
-        "macos_arm64": "694e3be8f2180a67602e781fcbde5c0241d1b5951300962a04d5e695ead7db28",
-    },
-    "25.6.0.dev2025082505": {
-        "linux_aarch64": "7ded0c7fb541ced6feacb29fa202242b51e628362d9c4ae32edd02479cbe21fe",
-        "linux_x86_64": "a3cf93ce991a0d4b162105e0fc4fbeb6edabc55b7c5457796161d055cdb1ccfd",
-        "macos_arm64": "439cd3d0ed19e27d623dc2a292c5356f4ccc1c89f0044f073caf3a23f2759b26",
+    "0.25.7.0.dev2025101005": {
+        "linux_aarch64": "ea10104453b8fe04398afaf78815f988bb12f824e1876ebbc16c3ef893d7568b",
+        "linux_x86_64": "5769a8930c9dddc621ba3da2ac088dd892bcc63fec0aa5f1645aa9c905247019",
+        "macos_arm64": "864e63f4a07af8387837e6c3f130d60fa1bc5ab66e5fc4815751ec25ebd37510",
     },
 }
 _PLATFORM_MAPPINGS = {