Minor: add comments explaining bad MSRV, output in json (#6857)

* Minor: add comments explaining bad MSRV

* purposely introduce msrv brek

* output in JSON format

* Revert "purposely introduce msrv brek"

This reverts commit 61872b6.

Author: alamb

.github/workflows/rust.yml

@@ -113,7 +113,7 @@ jobs:
         run: cargo fmt --all -- --check
 
   msrv:
-    name: Verify MSRV
+    name: Verify MSRV (Minimum Supported Rust Version)
     runs-on: ubuntu-latest
     container:
       image: amd64/rust
@@ -127,13 +127,19 @@ jobs:
         run: cargo update -p ahash --precise 0.8.7
       - name: Check arrow
         working-directory: arrow
-        run: cargo msrv --log-target stdout verify
+        run: |
+          # run `cd arrow; cargo msrv verify` to see problematic dependencies
+          cargo msrv verify --output-format=json
       - name: Check parquet
         working-directory: parquet
-        run: cargo msrv --log-target stdout verify
+        run: |
+          # run `cd parquet; cargo msrv verify` to see problematic dependencies
+          cargo msrv verify --output-format=json
       - name: Check arrow-flight
         working-directory: arrow-flight
-        run: cargo msrv --log-target stdout verify
+        run: |
+          # run `cd arrow-flight; cargo msrv verify` to see problematic dependencies
+          cargo msrv verify --output-format=json
       - name: Downgrade object_store dependencies
         working-directory: object_store
         # Necessary because tokio 1.30.0 updates MSRV to 1.63
@@ -143,4 +149,6 @@ jobs:
           cargo update -p url --precise 2.5.0
       - name: Check object_store
         working-directory: object_store
-        run: cargo msrv --log-target stdout verify
+        run: |
+          # run `cd object_store; cargo msrv verify` to see problematic dependencies
+          cargo msrv verify --output-format=json