Fix various misspellings of "corpora" & improve script comments

A misspelling in the https://github.com/gitpython-developers/qa-assets
repository is still present here. It will need to be fixed in that
repository first.

"corpora" is a difficult word to spell consistently I guess. This made
for a good opportunity to improve the phrasing of two other comments at
at least.

Based @EliahKagan's suggestion and feedback on:
#1901

fuzzing/oss-fuzz-scripts/build.sh

@@ -4,7 +4,7 @@ set -euo pipefail
 
 python3 -m pip install .
 
-# Directory to look in for dictionaries, options files, and seed corpa:
+# Directory to look in for dictionaries, options files, and seed corpora:
 SEED_DATA_DIR="$SRC/seed_data"
 
 find "$SEED_DATA_DIR" \( -name '*_seed_corpus.zip' -o -name '*.options' -o -name '*.dict' \) \
@@ -27,7 +27,7 @@ find "$SRC/gitpython/fuzzing" -name 'fuzz_*.py' -print0 | while IFS= read -r -d
       # If a dictionary file for this fuzzer already exists and is not empty,
       # we append a new line to the end of it before appending any new entries.
       #
-      # libfuzzer will happily ignore multiple empty lines in a dictionary but crash
+      # LibFuzzer will happily ignore multiple empty lines in a dictionary but fail with an error
       # if any single line has incorrect syntax (e.g., if we accidentally add two entries to the same line.)
       # See docs for valid syntax: https://llvm.org/docs/LibFuzzer.html#id32
       echo >>"$output_file"

fuzzing/oss-fuzz-scripts/container-environment-bootstrap.sh

@@ -34,7 +34,7 @@ download_and_concatenate_common_dictionaries() {
   done
 }
 
-fetch_seed_corpra() {
+fetch_seed_corpora() {
   # Seed corpus zip files are hosted in a separate repository to avoid additional bloat in this repo.
   git clone --depth 1 https://github.com/gitpython-developers/qa-assets.git qa-assets &&
     rsync -avc qa-assets/gitpython/corpra/ "$SEED_DATA_DIR/" &&
@@ -45,12 +45,13 @@ fetch_seed_corpra() {
 # Main execution logic #
 ########################
 
-fetch_seed_corpra
+fetch_seed_corpora
 
 download_and_concatenate_common_dictionaries "$SEED_DATA_DIR/__base.dict" \
   "https://raw.githubusercontent.com/google/fuzzing/master/dictionaries/utf8.dict" \
   "https://raw.githubusercontent.com/google/fuzzing/master/dictionaries/url.dict"
 
 # The OSS-Fuzz base image has outdated dependencies by default so we upgrade them below.
 python3 -m pip install --upgrade pip
-python3 -m pip install 'setuptools~=69.0' 'pyinstaller~=6.0' # Uses the latest versions know to work at the time of this commit.
+ # Upgrade to the latest versions known to work at the time the below changes were introduced:
+python3 -m pip install 'setuptools~=69.0' 'pyinstaller~=6.0'