Upgrade toolchain to 2025-04-03 (#3988)

Culprit PR: rust-lang/rust#139102

Resolves  #3986

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 and MIT licenses.

Author: carolynzech

rust-toolchain.toml

@@ -2,5 +2,5 @@
 # SPDX-License-Identifier: Apache-2.0 OR MIT
 
 [toolchain]
-channel = "nightly-2025-04-02"
+channel = "nightly-2025-04-03"
 components = ["llvm-tools", "rustc-dev", "rust-src", "rustfmt"]

tests/coverage/abort/expected

@@ -14,7 +14,7 @@
   14|    1|         }\
   15|    1|         if i == 2 {\
   16|     |             // This should never happen.\
-  17|    0|             ```process::exit(1)''';\
+  17|    0|             ```process::exit'''(1);\
   18|    1|         } \
   19|     |     }\
   20|    0|     ```assert!'''(false, ```"This is unreachable"''');\

tests/coverage/known_issues/variant/expected

@@ -16,12 +16,12 @@
   16|    1| fn print_direction(dir: Direction) {\
   17|     |     // For some reason, `dir`'s span is reported as `UNCOVERED` too\
   18|    0|     match ```dir''' {\
-  19|    0|         Direction::Up => ```println!("Going up!")''',\
-  20|    0|         Direction::Down => ```println!("Going down!")''',\
+  19|    0|         Direction::Up => ```println!("Going up!"'''),\
+  20|    0|         Direction::Down => ```println!("Going down!"'''),\
   21|    1|         Direction::Left => println!("Going left!"),\
-  22|    0|         Direction::Right if 1 == ```1 => println!("Going right!")''',\
+  22|    0|         Direction::Right if 1 == ```1 => println!("Going right!"'''),\
   23|     |         // This part is unreachable since we cover all variants in the match.\
-  24|    0|         _ => ```println!("Not going anywhere!")''',\
+  24|    0|         _ => ```println!("Not going anywhere!"'''),\
   25|     |     }\
   26|     | }\
   27|     | \