Bring back MINIMUM_SUPPORTED_TOOLCHAIN_VERSION to 1.78.0

Author: ShoyuVanilla

crates/rust-analyzer/src/lib.rs

@@ -14,7 +14,7 @@ extern crate ra_ap_rustc_type_ir as rustc_type_ir;
 /// Any toolchain less than this version will likely not work with rust-analyzer built from this revision.
 pub const MINIMUM_SUPPORTED_TOOLCHAIN_VERSION: semver::Version = semver::Version {
     major: 1,
-    minor: 90,
+    minor: 78,
     patch: 0,
     pre: semver::Prerelease::EMPTY,
     build: semver::BuildMetadata::EMPTY,