docs: api -> API

Reviewed-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7060>
diff --git a/docs/envvars.rst b/docs/envvars.rst
index 863e378..bc43d1e 100644
--- a/docs/envvars.rst
+++ b/docs/envvars.rst
@@ -39,7 +39,7 @@
    if set, disables Intel SSE optimizations
 ``MESA_NO_ERROR``
    if set to 1, error checking is disabled as per ``KHR_no_error``. This
-   will result in undefined behavior for invalid use of the api, but
+   will result in undefined behavior for invalid use of the API, but
    can reduce CPU use for apps that are known to be error free.
 ``MESA_DEBUG``
    if set, error messages are printed to stderr. For example, if the