sysutils/yazi: Update to 26.8.15

• Define the environment variable VERGEN_GIT_SHA, otherwise the build stage fails with error:

error: environment variable VERGEN_GIT_SHA not defined at compile time
--> yazi-version/src/lib.rs:3:76

|

3 | pub fn version() -> &'static str { concat!(env!("CARGO_PKG_VERSION"), " ", env!("VERGEN_GIT_SHA")) }

|                                                                            ^^^^^^^^^^^^^^^^^^^^^^
|
= help: use `std::env::var("VERGEN_GIT_SHA")` to read the variable at run time

error: environment variable VERGEN_GIT_SHA not defined at compile time
--> yazi-version/src/lib.rs:9:3

|

9 | env!("VERGEN_GIT_SHA"),

|         ^^^^^^^^^^^^^^^^^^^^^^
|
= help: use `std::env::var("VERGEN_GIT_SHA")` to read the variable at run time

warning: yazi-version@26.8.15: not within a suitable 'git' worktree!
warning: yazi-version@26.8.15: Unable to set VERGEN_GIT_SHA
error: could not compile yazi-version (lib) due to 2 previous errors

ChangeLog: https://github.com/sxyazi/yazi/blob/main/CHANGELOG.md#v26815
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