[rust] Set GITHUB_ACTIONS=true on rust builders

With rust-lang/rust#110115, some path length reduction features are only enabled on CI. We fake that with GITHUB_ACTIONS=true.

Bug: 1441182
Change-Id: I09dc11459f1a0d941846075b52ada717ef0e2a9d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4496591
Commit-Queue: Arthur Eubanks <[email protected]>
Reviewed-by: danakj <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1138102}
NOKEYCHECK=True
GitOrigin-RevId: 9fc3ea506f7d471c1aed19e587df7324f7583ac1

Author: aeubanks

build_rust.py

@@ -430,6 +430,12 @@ def __init__(self, zlib_path, libxml2_dirs, build_mac_arm,
         # Cargo normally stores files in $HOME. Override this.
         self._env['CARGO_HOME'] = CARGO_HOME_DIR
 
+        # https://crbug.com/1441182
+        # Pretend we're a CI, since some path length reduction features are
+        # only enabled for CI. Otherwise some tests fail when the rust src
+        # directory name length is too long.
+        self._env['GITHUB_ACTIONS'] = 'true'
+
     def configure(self, build_mac_arm, x86_64_llvm_config,
                   aarch64_llvm_config):
         # Read the config.toml template file...