Rollback to rust compiler 1.64.

cc rustwasm/gloo#423 (comment)

Author: langyo

.github/workflows/main-checks.yml

@@ -67,7 +67,7 @@ jobs:
       fail-fast: false
       matrix:
         toolchain:
-          - 1.67.0
+          - 1.64.0
           - stable
 
     steps:
@@ -116,7 +116,7 @@ jobs:
       fail-fast: false
       matrix:
         toolchain:
-          - 1.67.0
+          - 1.64.0
           - stable
           - nightly
 
@@ -153,7 +153,7 @@ jobs:
       fail-fast: false
       matrix:
         toolchain:
-          - 1.67.0
+          - 1.64.0
           - stable
           - nightly
     steps: